Treatment of Primary Pigmented Nodular Adrenocortical Disease

Abstract

Primary pigmented nodular adrenocortical disease (PPNAD) is a rare cause of adrenocorticotropin hormone (ACTH)-independent Cushing’s syndrome (CS), which mainly occurs in children and young adults. Treatment options with proven clinical efficacy for PPNAD include adrenalectomy (bilateral or unilateral adrenalectomy) and drug treatment to control hypercortisolemia. Previously, the main treatment of PPNAD is bilateral adrenal resection and long-term hormone replacement after surgery. In recent years, cases reports suggest that unilateral or subtotal adrenal resection can also lead to long-term remission in some patients without the need for long-term hormone replacement therapy. Medications for hypercortisolemia, such as Ketoconazole, Metyrapone and Mitotane et.al, have been reported as a preoperative transition for in some patients with severe hypercortisolism. In addition, tryptophan hydroxylase inhibitor, COX2 inhibitor Celecoxib, somatostatin and other drugs targeting the possible pathogenic mechanisms of the disease are under study, which are expected to be applied to the clinical treatment of PPNAD in the future. In this review, we summarize the recent progress on treatment of PPNAD, in which options of surgical methods, research results of drugs acting on possible pathogenic mechanisms, and the management during gestation are described in order to provide new ideas for clinical treatment.

Introduction

Primary pigmented nodular adrenocortical disease (PPNAD) is a rare cause of adrenocorticotropin hormone (ACTH)-independent Cushing’s syndrome (CS) and is characterized by small, black and brown pigmented micronodules in adrenal cortex. PPNAD mainly occurs in children and young adults. The incidence of PPNAD is unknown at present ¹ . PPNAD accounts for only about 1.1–1.8% of all causes of CS ^{2 3} . It may be isolated or associated with Carney complex (CNC). About 10% of patients with PPNAD without familial history or other manifestations of CNC, are generally termed as isolated PPNAD (i-PPNAD) ⁴ . CNC is a rare autosomal dominantly inherited multiple neoplasia syndrome characterized by spotty skin pigmentation, multiple endocrine neoplasia, and myxomas ⁵ . It is most frequently caused by mutations in the type 1a regulatory subunit gene of protein kinase A (PKA) ( PRKAR1A ), and approximatively 30% of cases occur sporadically. Clinical manifestations of CNC include lentigines, blue nevus, myxomas in the heart, skin, and breast, pituitary tumors, adrenocortical tumors, and thyroid neoplasms. PPNAD and the consequent ACTH-independent Cushing’s syndrome is one of the most common endocrine manifestations of CNC, accounting for about 25–60% of CNC patients ^{6 7} .

Hypercortisolism in PPNAD can be overt, subclinical, cyclic or atypical. And adrenal imaging is also often non-specific, which makes the diagnosis and treatment of the disease difficult ^{8 9 10 11} . In the last two decades, much progress has been made in describing the various forms, clinical manifestations, and pathogenesis of PPNAD. However, there is still controversy regarding the treatment of the disease. Treatment options with proven clinical efficacy for PPNAD included adrenalectomy (bilateral or unilateral adrenalectomy) and drug treatment to control hypercortisolemia. The preferred treatment is surgery. Bilateral adrenalectomy is the universal recommended option, which will cause permanent adrenal insufficiency and require a life-long hormone replacement therapy ¹² . In recent years, some authors considered that unilateral adrenalectomy or subtotal adrenalectomy can also let selected patients to obtain long-term remission without hormone replacement therapy, so that patients have a better quality of life ^{13 14 15} . As PPNAD often leads to mild, occult or atypical Cushing’s syndrome, drug therapy may be a good candidate. In medical treatment, Ketoconazole, Metyrapone, Mitotane and other drugs can be used to treat hypercortisolemia for patients who have severe hypercortisolemia before surgery and refuse to undergo further surgery or who have surgical contraindications ¹⁶ . In addition, a number of promising drugs are being studied and may be used in the clinic in the future. Along with the basic research of PPNAD, scholars found that there were several alternative drugs associated with the possible mechanism targets of the disease: tryptophan hydroxylase inhibitor, 5-hydroxytryptamine receptor antagonist, COX2 inhibitor celecoxib and somatostatin, etc. ^{17 18 19} . These drugs are promising, but most of them only are proven in animal studies, and further research is needed to illustrate whether they can be used in the clinic.

PPNAD is now better recognized, an increasing number of endocrinologists and urologists were aware of its numerous manifestations and the need for effective management. Furthermore, the management of some special groups, such as children and pregnant women, need multidisciplinary cooperation. Appropriate treatment strategy and follow-up management are important to prognosis of disease. In this review, we will summarize the update of diagnosis and treatment of PPNAD, including treatment experience on patients during gestation, and results of studies on new type drugs acting on new molecular targets.

Clinical Characteristics of PPNAD

PPNAD patients are generally younger. The age of PPNAD patients associated with CNC appeared to be bimodally distribution, with a few appearing in the first 2–3 years and most in the twentieth and thirtieth decades ²⁰ . Among a total of 212 patients with PPNAD, the prevalence was significantly higher in women than in men (71 vs. 29%). The median age of PPNAD diagnosis was 34 years, and women were diagnosed at a younger age than men (30 years vs. 46 years). Such gender difference became apparent after puberty ²¹ .

CS usually starts insidiously, and the main features are hypertension, weight gain, and growth restriction in children, although it is not seen in all patients. Typical features also include osteoporosis, proximal muscle weakness, wide purple striae, full moon face, central obesity, irregular menstruation in women, hirsutism, acne, decreased cognitive function, and so on ^{22 23} . According to previous literature, hypercortisolism in PPNAD can be overt, subclinical, cyclic or atypical ^{8 9 10 11} . Due to the variable Cushing’s syndrome phenotypes of PPNAD, its symptoms and signs may not be obvious. Patients always visit doctors repeatedly until the diagnosis of ACTH-independent CS can be clearly diagnosed ¹² . Whether these different CS phenotypes are related to the genotype of PPNAD remains to be further explored.

Osteoporosis and osteoporotic fractures are more common in patients with PPNAD compared with other causes of Cushing’s syndrome. In a 10-year retrospective study of 1652 Chinese Cushing’s syndrome patients, osteoporotic fractures were observed more frequently in PPAND than in adrenocortical adenoma (ADA) and primary bilateral macronodular adrenal hyperplasia (PBMAH) patients (26.7 vs. 9.0 vs. 4.9%) ³ . In another Chinese PPNAD cases (25 patients), PPNAD patients are more likely to develop osteoporosis than ADA patients (78.3 vs. 48.0%), while there are no differences between PPNAD and PBMAH patients ⁹ . In addition, some patients are accompanied by hyperandrogenemia, with hirsutism and irregular menstruation as the main symptoms ^{8 24 25} . In a case series of 6 patients from India, one patient had CS associated with symptoms of hyperandrogenism (hirsutism and irregular menses) ⁸ .

Since the majority of PPNAD patients are associated with CNC, patients usually have clinical manifestations associated with CNC, such as spotty skin pigmentation, heart myxoma, skin myxoma. And many patients have a family history of CNC or PPNAD ^{7 26} .

Although CS is rare in children, it can lead to significant morbidity and even mortality. CS should be diagnosed early by clinician ²⁷ . PPNAD mainly occurs in late childhood or youth, and is very rare in infancy, the reported youngest patients are only 15 months ⁸ . Bilateral adrenal resection and replacement therapy were the most common treatment strategies ^{28 29} , Ketoconazole and other drugs can be used for transition before surgery ⁸ . They always showed catch-up growth and improvement in the BMI after adrenalectomy ^{8 28 30} . PPNAD may be a signal of CNC, so patients with dominant CS at a younger age may requires genetic testing and long-time follow-up.

PPNAD is very rare in infancy, whereas CS associated with McCune – Albright syndrome (MAS) is usually in infancy. MAS is a sporadic heterogeneous disorder caused by an activating mutation in GNAS , which encodes the alpha subunit of the Gs G-coupled protein receptor ³¹ . It is characterized by congenital polyostotic fibrous bone dysplasia, café-au-lait skin plaques, precocious puberty and other endocrine disorders. About 7.1% of patients can present with CS, which is usually severe, and is also associated with other endocrine dysfunction, such as hyperthyroidism and precocious puberty ³² .

Adrenal causes of CS, such as PBMAH and adrenal cortical adenoma, may be closely associated with anomalous adrenal hormone receptors, especially G-coupled protein receptors, such as the gastric inhibitory polypeptide (GIP) receptor, the luteinizing hormone/human chorionic gonadotropin (LH/HCG) receptor, vasopressin (AVP) receptor, and the beta-adrenergic receptor ³³ . These aberrant adrenal hormone receptors are functionally associated with steroidogenesis. Although less reported in PPNAD, aberrant 5-HT receptors have recently been found to be expressed in PPNAD ¹⁷ . The detection of abnormal adrenergic hormone receptors provides a new target for treatment.

Diagnosis of PPNAD

The diagnosis of PPNAD is challenging, especially for patients without other manifestations of CNC or family history due to: 1) clinical manifestations may not be obvious, atypical, and progress slowly; 2) laboratory tests can be normal during the non-secretory period of periodic CS; 3) those without CNC-related clinical manifestations (skin pigmentation, myxoma, etc.) and family history which effect judgement; and 4) it is difficult to accurately find small nodules on CT.

First, the diagnosis of CS should be established. After excluding exogenous glucocorticoid exposure, initial screening tests include urine free cortisol (UFC), late night salivary cortisol, 1 mg overnight dexamethasone suppression test (DST) and 2 mg/d for 48 hours DST ³⁴ . The dexamethasone-CRH test or the midnight serum cortisol test can be used as subsequent evaluation to establish the cause of CS in patients with concordantly positive results from two different initial tests ³⁴ .

Adrenal imaging should be evaluated in patients with suspicious adrenal cause CS. In PPNAD, computed tomography (CT) imaging examinations may show normal size adrenal glands and several small bead-like nodules ^{22 35} . But ‘normal’ imaging is often reported too ¹⁰ . CT with slice thickness of 3 mm or less may be helpful for diagnosis ³⁶ . Single-photon emission computed tomography (SPECT-CT) with the use of iodomethyl-norcholesterol (I-131) showed bilateral glands uptake was increased ²⁵ . It supported the diagnosis of PPNAD. In addition, adrenal cortical imaging with (6–131I) iodomethyl-19 cholesterol-lowering (NP-59) also can be an optional imaging examination. Vezzosi et al. compared CT scans and adrenal cortical imaging with (6–131I) iodomethyl-19 cholesterol-lowering (NP-59) in 17 patients with diagnosed PPNAD. NP-59 imaging showed bilateral adrenal uptake in all patients, and asymmetric uptake was observed in 59% of patients ³⁷ . Besides, bone scintigraphy will help identify bone lesions associated with MAS ³⁸ .

Laboratory examination often show that patients with overt CS have ACTH-independent cortisol secretion hypercortisolism unrelated to ACTH and lack of cortisol diurnal rhythm. However, laboratory tests may be normal during the non-secretory period of periodic CS. It is worth noting that patients with PPNAD often appear an abnormal increase in urinary free cortisol during the Liddle test ³⁹ . This increase in urinary glucocorticoid excretion following dexamethasone administration is one of the diagnostic criteria for CNC. But recently, a prospective study showed that only 39 percent of patients with confirmed or probable PPNAD had an abnormally elevated UFC ⁴⁰ . In 2018, for the first time Chen et al. proposed to distinguish PPNAD from bilateral macronodular adrenal hyperplasia and adrenal cortical adenoma (ADA) by using the ratio of UFC to pre-HDDST 24 hours after high-dose dexamethasone inhibition test (HDDST). When 24-hour UFC (post-H-DEX)/UFC (pre-H-DEX) was>1.08, the sensitivity and specificity were 84.0 and 75.6%, respectively ⁹ . In addition, adrenal tissue ACTH immunohistochemistry will help identify the presence of ACTH paracrine secretion ⁴¹ .

ACTH is a regulator of androgen secretion from the adrenal cortex. Due to the inhibitory effect of excessive cortisol secretion on ACTH, the dehydroepiandrosterone (DHEAS) of adrenal CS patients were often lower than those of healthy individuals ¹⁷ . According to previous reports of patients with PPNAD, laboratory results showed frequent decreases in serum DHEAS levels ¹⁸ , and some patients showed overproduction of testosterone and normal DHEAS ⁶ . Overproduction of androgens by PPNAD-associated adenomas leading to virilization and infertility has also been reported in the literature ¹⁹ .

ACTH is a regulator of androgen secretion from the adrenal cortex. Due to the inhibitory effect of excessive cortisol secretion on ACTH, the dehydroepiandrosterone (DHEAS) of adrenal CS patients were often lower than those of healthy individuals ⁴² . According to previous reports of patients with PPNAD, laboratory results showed frequent decreases in serum DHEAS levels ²⁵ , and some patients showed overproduction of testosterone and normal DHEAS ²⁴ . Overproduction of androgens by PPNAD-associated adenomas leading to virilization and infertility has also been reported in the previous literature ⁴³ .

Both CNC and PPNAD can be associated with inactivating mutations of the PRKAR1A gene. In 353 patients with PPNAD or CNC, 73% carried 80 different PRKAR1A mutations ²¹ . Such inactivating PRKAR1A germline mutations are also common in i-PPNAD ^{24 44} . In addition, mutations in PDE11A ⁴⁵ and PDE8B ⁴⁶ are described for PPNAD. Somatic defects in PRKAR1A gene ⁴⁷ , and β-catenin gene ( CTNNB1 ) ⁴⁸ have been also observed in PPNAD patients, which has potential clinical and genetic significance. The study of genetic mutations in adrenal tissue will help to identify such somatic mutations. And genetic testing may be of great help in diagnosing PPNAD.

Adrenalectomy

Bilateral adrenalectomy

Bilateral adrenalectomy is the universal recommended surgical type for PPNAD treatment because of its feature for involvement of bilateral adrenal glands ^{8 12 49 50 51} . Clinical Practice Guidelines for the treatment of CS from Endocrine Society suggested that laparoscopic bilateral adrenalectomy is the definite treatment for PPNAD ⁵² . Laparoscopic surgery can be performed as transabdominal or retroperitoneal approach, both of which have significant advantages over open surgery, including a clear field of vision, small incisions, less bleeding, and shorter hospital stays. The retroperitoneal approach, which can avoid abdominal stimulation has shorter operative time, fewer complications and less postoperative pain. But it has a smaller workspace and may increase intraocular pressure due to the need for prone position ⁵³ . The advantages of bilateral adrenalectomy are that it rapidly cures CS, has low risk of recurrence, and is suitable for patients of all ages ^{8 28 54} . Bilateral adrenalectomy was performed in most patients presenting with overt CS. According to the current literatures, most of patients have biochemical remission after bilateral adrenalectomy, and the corresponding symptoms can disappear. The children always catch-up with growth, and the weight of patients can return to normal, and the Cushing appearance can disappear. Most of the patients were followed up for a short period of time. It is conceivable that bilateral adrenalectomy will cause permanent adrenal insufficiency and require a life-long careful glucocorticoid and mineralocorticoid replacement therapy. Such patients are prone to acute adrenal crisis as a complication especially under stress or infection, and may have a lower quality of life, so they have to be good compliance ^{8 12 15 35} . Unilateral total adrenalectomy associated with contralateral partial adrenal (adrenal-sparing surgery) has been observed to achieve good treatment results in PBMAH ⁵⁵ . This approach avoids the need for lifelong steroid replacement in most cases and has a low rate of adrenal insufficiency and recurrence ⁵⁶ . It may be a potential surgery approach for PPNAD.

In 31 patients with adrenal hyperplasia (MAH) or PPNAD who underwent bilateral adrenalectomy, 30 (97%) patients are cured biochemically ¹² . These patients had complete resolution for Cushing’s syndrome symptoms at 9 to 12 months postoperatively. Six patients in their cases presented with hypertension, and all were cured or improved after surgery. Five of them were able to discontinue all antihypertensive drugs, and the remaining one required only one antihypertensive drug. In the case series of Memon et al. on a mean age of 8.2 years, 5 patients are cured after bilateral adrenalectomy, and 1 of them die about 2 years after surgery probably caused by an adrenal crisis. All patients showed improvement in height post-surgery ⁸ . Two adolescent brothers with complaints of weight gain and growth retardation had typical Cushing’s syndrome manifestations: hypertension, moon-shaped face, facial plethora, centripetal obesity, and red-purple skin striae. One month after bilateral adrenalectomy, they lost 5–6 kg of weight their skin textures fades and there was a reduction in the facial plethora. And their blood pressure, lipids and heart ejection fraction were improved ²⁸ . A 20-year-old woman presenting with overt CS had bilateral avascular necrosis of the femoral heads. After bilateral adrenalectomy, her presentation of cortisol excess improved, and her femoral head necrosis resolved without orthopedic intervention with 1-year follow-up ⁵⁷ .

Unilateral adrenalectomy

In recent years, more studies have shown that unilateral adrenal resection can achieve remission of long-term symptoms and biochemical for some patients without adrenal insufficiency ⁵¹ . Some case reports ^{58 59} and cases series proved the feasibility and effectiveness of unilateral adrenalectomy ^{10 13 60} . Most patients acquired biochemical remission and disappearance of clinical symptoms after unilateral adrenalectomy. But some patients reappear with symptoms of hypercortisolism after surgery, usually less severe than at the time of presentation. And most patients with recurrence undergo contralateral resection, while some are treated with medication.

A 16-year-old female patient with complaints of weight gain and irregular menstruation had a preoperative iodocholesterol scintigraphy showing unilateral uptake of the left adrenal gland. She underwent left adrenalectomy. After 10 months of follow-up, she had significant weight loss, disappearance of the features of CS and biochemical remission ⁵¹ . Xu et al. reviewed 13 PPNAD patients who underwent unilateral adrenalectomy, of whom only 1 patient recurred with a requirement of contralateral adrenal resection, while the rest achieved remission (Median follow-up time: 47 months) ¹³ . Kyrilli et al. summarized the patients with unilateral adrenal resection in the literature. There were 24 cases with unilateral adrenalectomy, followed by contralateral resection in 5 cases, with the duration of contralateral resection ranging from 2 months to 25 years ¹⁴ .

Cohen et al. reported a case of successful pregnancy after unilateral adrenal resection without adrenal hypofunction during pregnancy, indicating that unilateral adrenal resection may be considered as an option for women with fertility needs ⁵⁹ . There were two 15-year-old patients with complaints of weight gain and growth retardation, with typical manifestations of hypercortisolism on examination (central obesity, hirsutism, purplish streaks, facial acne). They underwent unilateral adrenalectomy. 5–6 months postoperatively, they had significant clinical and biochemical improvement, weight loss, accelerated growth, and regression of skin streaks and acne. One required HC replacement for a short period of time and one not required HC replacement. Then they reappeared with CS symptoms and laboratory tests suggesting loss of cortisol circadian rhythm, so contralateral adrenalectomy was performed at 8 and 10 months postoperatively ⁶¹ .

Bilateral adrenocortical hyperplasia (BAH) mainly includes Primary Bilateral Macronodular adrenocortical hyperplasia (PBMAH) and PPNAD ⁶² . Studies have shown that unilateral adrenalectomy improves clinical symptoms and biochemical status successfully for PBMAH for adult patients, particularly for patients with asymmetric hyperplasia and mildly phenotypes ^{62 63 64} . Similar to PBMAH, PPNAD is often manifested as mild to moderate CS. That suggested that unilateral resection for PPNAD may also be a feasible approach.

Some patients have bilateral adrenal nodular hyperplasia with the presence of macronodules. Research studies of Vezzosi et al. about Adrenal [6β- ¹³¹ I]-iodomethyl-19-norcholesterol] (NP-59) scintigraphy revealed that asymmetrical adrenal uptake associated with macronodules in 10 of 17 patients (59%) ³⁷ . In those patients with unilateral greater nodular hyperplasia, selective resection of the side with greater nodules may be a good option. There are twins female patients with PPNAD from Belgium who under unilateral adrenalectomy have ongoing clinical and biochemical remissions without any adrenal insufficiency after 3 years and 18 months follow-up after surgery, respectively ¹⁴ . Unilateral adrenalectomy was chosen because the symptoms were mild and asymmetric bilateral adrenal uptake or size was shown on imaging ( ¹³¹ I iodomethyl-norcholesterol scintigraphy coupled with single-photon emission computed tomography (SPECT)/CT Adrenal CT scan) ¹⁴ .

It seems unilateral adrenalectomy can relieve the symptoms of mild to moderate CS without causing adrenocortical insufficiency. When NP-59 scintigraphy or (SPECT)/CT scan revealed asymmetrical adrenal uptake ³⁷ , selective resection of the side with prevalent uptake may be a good option ¹⁴ . But scintigraphy is not available in many countries. Adrenal volume measurement, adrenal vein sampling are also modalities that can substitute scintigraphy. Clinicians should also consider the possibility that unilateral resection may not be a complete cure and may require a second operation. There is also a case showed that adrenal crisis occurred during a viral infection 3 weeks after unilateral adrenalectomy ⁵⁰ . But we thought the probability for adrenal crisis of unilateral adrenalectomy is much lower than bilateral resection. Most adrenalectomies are performed by laparoscopy with less trauma. For patients who have the possibility of remission after resection of one side, they and their doctors may prefer to remove one side first and then remove the other side after recurrence. Compared with permanent adrenal insufficiency caused by bilateral adrenal resection, it may be better to selectively remove one side of the adrenal gland for patients with atypical or mild symptoms. In addition, genotypic - phenotypic correlation indicated that some gene mutation sites were associated with milder phenotypes, which may be a basis for determining surgical approaches, but further studies are needed ²¹ . Therefore, we suggested that clinicians should select unilateral or bilateral adrenal resection based on a comprehensive evaluation of the degree of increased cortisol, symptoms, preoperative imaging evaluation, and the patient’s willingness, to choose the surgical procedure with the best benefit. Due to the rarity of PPNAD, clinical studies about the treatment were limited, the indication and long-term efficacy of unilateral adrenal resection remained to be studied. If further studies could confirm the indications for unilateral adrenal resection, it may greatly improve the quality of life of patients without long-term hormone replacement on the basis of disease control.

Drug Therapy

Drugs that inhibit steroid production and action

There are several kinds of drugs to treat hypercortisolism as conservative managements. These include steroidogenic inhibitors (Metyrapone, Mitotane, Etomidate, LCI699) and glucocorticoid receptor antagonists (Mifepristone) ⁶⁵ . They can be used as preoperative transition for patients with severe hypercortisolemia or maintenance therapy for patients who refuse surgery ⁶⁵ . Medication is also needed for patients who are not cured completely after surgery ⁴⁴ .

If patients have severe hypercortisolemia preoperatively, they should receive adrenolytic medications for weeks preoperatively ¹² . In the literature, Ketoconazole can as a bridge therapy before surgery ^{8 25} . It is worth noting that Ketoconazole has potential side effects such as liver enzyme elevation, gastrointestinal discomfort, androgen reduction and pruritus ⁶⁶ . Therefore, it is not generally preferred for men, and it should be used under liver enzyme monitoring ⁶⁷ . Ketoconazole treatment has been used successfully in several cases of CS pregnancy and did not cause birth defects to the fetus ^{68 69} . Fluconazole has been considered as an alternative to Ketoconazole ⁷⁰ . Navarro et al. reported case series in which a patient showed a significant decrease in urinary cortisol after 3 months of Fluconazole treatment. But he discontinued due to the side effects of pruritus and facial rash; Another patient remained on low-dose Metyrapone as maintenance therapy after unilateral adrenalectomy ⁴⁴ .

As for a patient who refused surgery, long-term and low-dose mitotane therapy (from 0.5 g/d to 4 g/d) was an effective method to correct hypercortisolism. The typical symptoms of Cushing’s syndrome and hyperandrogenism gradually subsided at two months from the beginning of the treatment. The size of the adrenal glands appeared to be reduced after 7 months adrenolytic treatment. The patient was still in remission after 122 months follow-up ¹⁶ .

Besides, Osilodrostat as an oral 11β-hydroxylase (CYP11B1) inhibitor, catalyzes the final step of cortisol synthesis. And it is administered less frequently than conventional drugs, with fewer adverse effects and fewer interactions with other drugs ^{71 72} . Phase III clinical trial results have confirmed its safety and efficacy in adult CS patients, and it may be a new option for the treatment of PPNAD.

New drugs targeting possible pathogenic mechanisms

The pathogenic mechanisms of PPNAD are still not clear up to now, a possible mechanism is that genetic events lead to structural activation of cAMP/PKA (cyclic adenosine monophosphate/protein kinase A) signal pathway ^{73 74} . The PKA consists of two molecules of regulatory (R) subunits bound to two molecules of catalytic (C) subunits. PRKAR1A as a tumor-suppressor gene located at 17q22–24 encodes the type 1a regulatory subunit of cAMP-dependent PKA ^{73 75} . Inactivation mutation of PRKAR1A cause premature stop codons through the nonsense-mediated mRNA decay (NMD). This process would lead to a truncated protein product which contributes to increased signal by PKA ^[76 . In addition, mutations in the phosphodiesterase PDE11A ⁴⁵ and PDE8 and the PKA catalytic subunit PRKACA gene ⁷⁷ are also detected in patients with PPNAD, and all of these gene events lead to structural activation of the cAMP/PKA signaling pathway, resulting in high glucocorticoid secretion independent of ACTH.

There are a number of drug candidates currently under study that target possible mechanisms of the disease, such as Rapamycin, Celecoxib, tryptophan hydroxylase inhibitors ( Fig. 1 ). These drugs have been proven in animal or in vitro tests, but there are no clinical studies have been reported.

Fig. 1.

Drug candidates under study that target possible mechanisms of PPNAD. One of pathogenic mechanisms of PPNAD is that genetic events lead to structural activation of cAMP/PKA signal pathway, resulting in high glucocorticoid secretion independent of ACTH. The mTORC1 pathway was activated by PKA signaling. Rapamycin is a mTOR inhibitor that acts on the PKA/mTOR pathway. Activated PKA signal leads to FLACs cannot be clear out and then morbid hyperplasia of adrenal cortical. Celecoxib can effectively reduce the proliferation of adrenal cortical cells induced by FLACs and thereby reduce glucocorticoid production. There is an illicit serotonergic stimulatory loop associated with hypercortisolemia because of cAMP/PKA pathway activation in adrenal tissues. Tryptophan hydroxylase inhibitors can reduce the stimulatory effect of 5-HT. Somatostatin analogs can reduce intracellular cAMP production and thus may reduce cortisol secretion in PPNAD. PPNAD, Primary pigmented nodular adrenocortical disease; cAMP/PKA, cyclic adenosine monophosphate/protein kinase A; mTORC1, the mammalian target of Rapamycin sensitive complex 1; FLACs, Fetal-like adrenal cortical cells; 5-HT, 5-hydroxytryptamine.

Rapamycin

The mammalian target of Rapamycin sensitive complex 1 (mTORC1) pathway was activated by PKA signaling in adrenal glands of specific PRKAR1A knockout mouse and human PPNAD tissues, leading to increased cell survival. PKA/mTOR activation was correlated with BAD (a member of the BCL-2 apoptotic family) hyperphosphorylation which may lead to apoptosis resistance and tumor formation. Rapamycin is an effective and selective mTOR inhibitor that acts on the PKA/mTOR pathway. Treatment with Rapamycin specifically sensitized ADKO adrenal cortical cells to dexamethasone-induced apoptosis in animal experiments, indicating its potential efficacy in the treatment of adrenal hyperplasia ^{78 79} .

Celecoxib

In specific PRKAR1A knockout mice, Sahut et al. observed that the atypical hyperplasia of fetal-like cortex at the corticomedullary junction. And such hyperplasia extended to the periphery over time. Fetal-like adrenal cortical cells (FLACs) caused by the lack of R1a cannot be clear out and then morbid hyperplasia of adrenal cortical ⁸⁰ . Celecoxib is a prostaglandin peroxidase synthase 2 (PTGS2) [also known as cyclooxygenase 2 (COX2)] inhibitor that is currently used to inhibit the growth of certain tumors. It is mainly related to the inhibition of prostaglandinE2 (PGE2), and the reduction of stem cell-like cells induced by this molecule ¹⁹ . Celecoxib can effectively reduce the proliferation of adrenal cortical cells induced by FLACs and thereby reduce glucocorticoid production, which has been verified in mice and human adrenal cells in vitro ⁸¹ .

Somatostatin analogues

Somatostatin (SST) analogues (SSA) like Octreotide can reduce intracellular cAMP production and thus may reduce cortisol secretion in PPNAD and other ACTH-independent CS patients. A short-term preliminary clinical study on the application of Octreotide in patients with PPNAD showed that the expression levels of somatostatin receptors (SSTRs) in PPNAD tissues were significantly higher than those in normal adrenal glands. But short-acting SSA Octreotide had no significant effect on cortisol secretion in patients with PPNAD. However, because of the sample size of this study was small, only Octreotide was used and further SSA-related studies with larger sample sizes may be possible in the future to further explore its effect on PPNAD ¹⁸ .

Tryptophan hydroxylase inhibitor

Bramet et al. found that adrenal tissues removed from PPNAD patients overexpress the key enzyme tryptophan hydroxylase type 2 (TPH2) and the 5-hydroxytryptamine receptors (5-HT4R, 5-HT6R and 5-HT7R) because of cAMP/PKA pathway activation, leading to an illicit serotonergic stimulatory loop associated with hypercortisolemia ¹⁷ . Later, Le Mestreet al. confirmed this by studying adrenal tissues exposed to high plasma ACTH levels for a long time and found that TPH and/or 5-HT4/6/7 receptors were overexpressed in tissues of different disease types. In addition, they found that 5-HT4R antagonists can reduce the stimulatory effect of 5-HT in vitro. It is suggested that tryptophan hydroxylase inhibitors may also be a promising drug for the treatment of PPNAD ⁸² .

Drug therapy is commonly used as a transition treatment preoperatively for patients with severe hypercortisolemia currently ⁶⁵ . The drugs targeting the specific mechanism of PPNAD are very promising. But they only have been proven in animal or in vitro tests. We expect these drugs to be proven clinically and look forward to the clear indications for drug therapy. Although there are still many problems to be solved in the treatment of PPNAD, we proposed a brief treatment strategy for PPNAD by summarizing the literature ( Fig. 2 ). We look forward to more studies that will tell us more about specific treatments.

Fig. 2.

treatment strategy for PPNAD.

Management of PPNAD During Gestation

Using “PPAND” and “pregnancy” as key words, we searched English literature published before May 2021 in PubMed database and found 3 cases with PPNAD during pregnancy ^{83 84 85} . There are 2 patients received Metyrapone to control hypercortisolemia during pregnancy ^{83 84} . All the 3 patients were successfully delivered by cesarean section, and the causes of delivery included preeclampsia and recurrent vaginal bleeding. All the infants survived after birth, and two infants developed respiratory distress syndrome and transient hyponatremia ( Table 1 ).

Table 1 Published reports of PPNAD during pregnancy.

Authors [Ref]	Patient age	Period	Therapy	Medication using during pregnancy	Perinatal morbidity	Birth weight (g)	Apgar scores (1 min, 5 min)	Fetal complications
Spaniol et al. 84	24	18–26 weeks	drug therapy, bilateral adrenalectomy 4 months postpartum	Metyrapone (500 mg/day)	preeclampsia	650	2, 6	NS
Schulz et al. 85	31	32 weeks	bilateral adrenalectomy postpartum	None	severe preeclampsia	1700	4, 8	moderate respiratory distress syndrome
Ralser et al. 83	31	26–31 weeks	drug therapy, remission at 6 weeks postpartum	Metyrapone (1000 mg/day)	recurrent vaginal bleeding	1740	8, 10	transient hyponatremia

IUGR: Intrauterine fetal growth restriction; NS: Not stated.

Hypercortisolism in PPNAD may be related to the high estradiol level during pregnancy. Catichaet.al. observed that estradiol can stimulate cortisol secretion in a dose-dependent manner with the absence of ACTH in vitro of PPNAD cells ⁸⁶ . Most drugs in the hypercortisolism treatment are contraindicated during pregnancy ^{87 88} . Metyrapone is an 11β-hydroxylase inhibitor that has been used safely during pregnancy ^{65 89} . It can reduce serum cortisol levels, but adrenocorticotropic hormone (ACTH) is stimulated with the decreased cortisol levels, which increases the production of mineralocorticoid, possibly leading to hypertension. This point should be vigilant in clinical practice ⁸⁹ . Due to the limited evidence reported in the literature, it should be used cautiously.

Due to high blood pressure, diabetes, weight gain and skin purple lines may also associate with pregnant, the diagnosis of CS during pregnancy is challenging. In addition, the physiological changes during pregnancy can also include the increase of serum cortisol and urine free cortisol ⁸⁹ . However, the loss of circadian rhythm of cortisol secretion and the significant increase of 24-hour urine free cortisol level are still helpful for the diagnosis of CS. If severe preeclampsia is diagnosed and blood pressure is difficult to control, pregnancy or delivery may need to be terminated promptly. In patients with a history of bilateral adrenal resection, hormone replacement must be monitored, and a stress dose of glucocorticoids administered at delivery. Unfortunately, there is no data on long-term follow-up of mothers and fetuses after completion of delivery of PPNAD. We have no idea about long-term remission. In conclusion, the pregnancy decision of PPNAD patients requires multidisciplinary cooperation. Due to the genetic characteristics of PPNAD and CNC, the fetus should be screened for genetic diseases after birth and a detailed follow-up strategy should be developed to detect and manage the possible related diseases at an early stage.

Conclusion

PPNAD is a rare disease with atypical symptoms and difficult clinical diagnosis. And the exact mechanism remains unclear. Surgery is the treatment of PPNAD, while the appropriate surgical methods should be selected according to individual circumstances. For patients who cannot receive surgical treatment or only have mild hypercortisolemia, drug treatment can be candidate. The drugs that may have therapeutic potential for PPNAD, such as tryptophan hydroxylase inhibitor, 5-HT receptor antagonist, COX2 inhibitor celecoxib and somatostatin, still need further clinical studies to confirm. Furthermore, we should pay attention to the management of PPNAD in children and pregnancy, strengthen interdisciplinary teamwork, and long-term follow-up should be conducted no matter what treatment plan is selected.