Endometriosis of the sciatic nerve masquerading as lumbar spondylosis in a 40-year-old Chinese woman

Abstract

A 40-year-old Chinese woman presented with a 4-year history of lower back pain and left lower leg sciatica. The patient had previously tried different modalities of treatments, including massage, acupuncture, ultrasound, alternative Bowen therapy and nonsteroidal anti-inflammatory drugs (NSAIDs), all of which only provided temporary relief. On presentation to a tertiary hospital, careful and comprehensive history taking found that the sciatica pattern of pain always coincided with menstruation. An MRI identified a thickened left sciatic nerve, with surgery confirming sciatic nerve endometriosis. The case highlights the importance of comprehensive history taking in accurately diagnosing a rare aetiology of sciatica with subsequent prompt surgical intervention to avoid severe disability as well as follow-up treatment to prevent recurrence.

Background

Endometriosis is the ectopic presence of endometrial glands and stroma.¹ This condition commonly affects the pelvic peritoneum, ovaries and rectovaginal septum.¹ Rarely, it can present as deep infiltrating endometriosis (DIE) on the sciatic nerve, resulting in a complex clinical picture. The relationship between the distribution and character of the pain to the menstrual cycle is a key finding.² This condition tends to present on the right side and is commonly accompanied by motor weakness and sensory loss.² While the examination is mostly unremarkable, a positive straight leg raise is commonly elicited.³ This case highlights the necessity of the thorough clinical reasoning required to arrive at this unlikely diagnosis.

Case presentation

A 40-year-old woman presented with a 4-year history of episodic lower back and calf pain associated with dysmenorrhoea, left lower limb weakness and dyspareunia. The patient initially presented to her local hospital with just sciatica and was treated with non-steroidal anti-inflammatory drugs with relief within 5–7 days at the local hospital. A CT scan of the lumbar spine at the local hospital showed no evidence of spinal canal stenosis and no nerve impingement. The most recent episode of left-sided sciatica was associated with severe period pain and left lower limb weakness. A detailed history described the pain that almost always worsened during the first 14 days of her menstrual cycle and partially alleviated with ovulation on the 15th day. She also described dyspareunia, which started 3 years ago.

The patient was not on any regular medication when she presented and did not have any known allergies. She had an artificial abortion 5 years ago, resulting in a 6-week history of pelvic inflammatory disease. Her family history was negative for any gynaecological conditions and other chronic diseases.

Her menstrual history was normal with a regular 28-day cycle and menses lasting 6–7 days. She denied any abnormal period-related abdominal pain and abnormal amount of period blood loss since menarche at the age of 11 years.

On examination, she had normal vital signs: temperature 36.5°C, pulse 80 beats/min regular, respiratory rate 20 breaths/min and blood pressure 100/70 mm Hg. She had left gluteus medius muscle tenderness on palpation and positive straight leg raising with the rest of the neurological examination being unremarkable. Cardiovascular, respiratory and abdominal examinations were all unremarkable.

Investigations

MRI of the pelvic, upper thigh and buttocks revealed a high signal density irregular patchy area in near the left piriformis and gluteus medius. The patchy areas were 25×21 mm with irregular borders. Contrast-enhanced imaging showed irregular patchy areas wrapped around the left thickened sciatic nerve (figure 1). The left sciatic nerve in contrast-enhanced imaging also demonstrated a confluent or continuous high signal intensity, irregular patchy areas over the left piriformis and gluteus medius muscles (figure 1). The right sciatic nerve, gluteus medius and piriformis were normal (figure 1).

Figure 1.

Points to MRI scan: contrast-enhanced imaging showing irregular areas around the left sciatic nerve, consistent with thickened sciatic nerve.

The interpretation of the imaging was most likely consistent with left sciatic nerve endometriosis.

MRI scan also showed adenomyosis and uterine fibroids. This was consistent with the subsequent transabdominal and transvaginal Doppler ultrasounds diagnosis of endometriosis, adenomyosis and uterine fibroids.

Differential diagnosis

The initial diagnosis was severe osteoarthritis of the lumbar spine with sciatica, based on distribution of pain described by the patient. Soft tissue tumour-like sarcoma invasion into the sciatic nerve was also considered for the focal tenderness of left gluteus medius muscle on palpation. MRI imaging did not support any of the above diagnosis. Left sciatic nerve endometriosis was certainly the ‘red flag’ disease considered based on the temporal pattern described by the patient, which was later confirmed on MRI imaging.

Treatment

Surgical exploration found severe endometriosis and three large uterine fibroids. DIE was found in three locations, including on the sigmoid colon with adhesion to the posterior wall of the uterus, on the sciatic foramen and on the piriformis and gluteus medius muscle. The DIE compressed on the sciatic nerve and its surrounding soft tissues, which was demonstrated on MRI imaging (figure 2).

Figure 2.

Intraoperative findings: deep infiltrating endometriosis was found in three locations as follows: (1) around the sigmoid colon with adhesion to the posterior wall of the uterus, (2) around the foramen sciatic with piriformis and gluteus medius muscle compression on the sciatic nerve and (3) around the sciatic nerve trunk.

The uterine fibroids and endometriosis in the pelvis were all surgically removed by laparoscopic approach with adequate exposure and careful dissection of the left sciatic nerve from the surrounding tissue using an ultrasonic scalpel to ensure the minimal disruption of the left sciatic nerve sheath on removal of the endometriosis. The management team decided to remove the uterine fibroids, alongside the endometriosis, due to their size.

The DIE outside the sciatic foramen into the left buttock was surgically removed by an open approach with a straight incision of approximately 15 cm created posteromedial to the left buttock. The left sciatic nerve was fully exposed by dissection along the space between the left sciatic nerve and the surrounding muscles using an ultrasonic scalpel to avoid any potentially functional damage to the left sciatic nerve, until all DIE around the nerve was adequately removed microscopically. The chief operators of this case were a gynaecologist and a plastic surgeon.

Outcome and follow-up

The left-sided sciatica completely resolved 2 weeks after surgery. The pain did not recur during menstruation in the following 4 months. However, a mild lower limb weakness distally on ankle dorsiflexion was present. Endocrine with hormonal therapy was discussed in preventing recurrence but was declined by the patient because of her intention with further conception and her concern with side effects. The patient has been advised to follow-up with a general practitioner or gynaecologist in her local hospital if there is recurrence of atypical extra-pelvic pain and discomfort associated with her regular menstruation.

The patient has also been referred to rehabilitation team in her local district to improve her mildly impaired ankle dorsiflexion. It was difficult at this stage to inform the patient whether the lower limb weakness was expected to resolve completely. There is currently no literature to support the management team in giving her a definitive answer. While it is hoped that it is a temporary condition, a permanent weakness may also occur. The plastic surgical team is actively following up with the patient every 6 months to monitor her progress.

Discussion

Endometriosis is defined as the presence of endometrial glands and stroma in ectopic sites, most commonly affecting the pelvic peritoneum, ovaries and rectovaginal septum.¹ The condition is seen in approximately 6%–10% of women of reproductive age, typically presenting with dysmenorrhea, dyspareunia, chronic pelvic pain, infertility and/or irregular uterine bleeding.^{1 4} DIE occurs when lesions infiltrate more than 5 mm deep to the peritoneum.⁵ This occurs in approximately 14% of cases of endometriosis, typically affecting the rectovaginal septum, rectum and rectosigmoid colon.⁴ Unfortunately, the diagnosis of endometriosis can be difficult, with a mean latency period of 6.7 years between the onset of symptoms to a definitive diagnosis.¹ Endometriosis has been infrequently observed infiltrating major pelvic nerves, causing sciatic neuropathy or lumbosacral plexopathy,³ as demonstrated in our case.

Endometriosis of the sciatic nerve is diagnosed with a thorough history and examination and confirmed on imaging. Typically, sciatic endometriosis presents as cyclical episodes of radiating pain along the sciatic nerve course, occurring in a temporal relationship with menstrual periods.³ This pain is characteristically present in the lower back, buttocks and down the back of the leg.² Other symptoms include motor weakness and sensory loss.² The haemorrhage in endometrial implants results in an inflammatory reaction, which consequentially causes nerve damage.⁶ Sciatic endometriosis is most commonly seen on the right side.⁶ This is thought to occur due to the positioning of the rectosigmoid colon in the left pelvic region, thus acting as a protective barrier to left pelvic tissues.^{6 7} In our case, the atypical presentation of non-specific lower back pain without radiation delayed the diagnosis for 4 years until the typical radiating pain along the sciatic nerve course synchronised with menstrual cycle, which raised the alarm to make the eventual diagnosis. The temporal relationship between the pain and menstrual periods seems to be critical in making the prompt diagnosis, which were demonstrated in a review of other cases of sciatic endometriosis.^{2 3 6} The pain experienced, can progress into constant pain, exacerbated with menstruation,² which is typically quite severe, with an average pain score varying between 8/10 and 10/10.⁶ Cutaneous numbness and gait disorders develop in advanced cases, where the endometriosis begins to involve and destroy a part of the sciatic nerve.⁶ In our case, the endometriosis did involve a part of the sciatic nerve consistent with persistently reduced left ankle dorsiflexion and mild gait abnormality at the 6-month review.

Physical examination is usually unremarkable, with neurological findings dependent on extent of nerve injury.³ Limitation of the straight leg raise test is common, as seen in this patient.⁸ Altered sensation along the L5 and S1 dermatome, with reduced power in the correlating myotome may also be seen.³

The investigation of choice for the assessment of endometriosis is MRI scan.³ Typically, lesions exhibit high signal intensity on T1 images and high and low signal intensity on T2 images.³ These findings, however, depend on the stage of the haemorrhage.³ CT and transvaginal/transrectal ultrasound may also be used.³ Our case highlighted the critical importance of MRI scan to confirm the diagnosis and guide further management. In a similar case of an endometrioma passing through the left greater sciatic foramen, compressing the sciatic nerve, CT, MRI and ultrasound were used to arrive at a clinical diagnosis.⁶ The 20-year-old patient presented with a 6-year history of severe dysmenorrhoea and a 4-month history of left lower limb dysfunction.⁶ CT and MRI showed a suspected intrapelvic and extrapelvic endometriotic cyst.⁶ Transvaginal ultrasound showed a cyst with homogenous dark area of liquid and clear borders, in the left pelvis.⁶ The cyst was laparoscopically removed and was confirmed to be endometriosis with postoperative pathology.⁶ A similar diagnostic process was used in a case of DIE of the rectovaginal septum.⁸ The 38-year old patient presented with primary infertility, chronic pelvic pain and dysmenorrhea.⁸ The 3-year history of pelvic pain and dysmenorrhea began when she stopped the contraceptive pill.⁸ She also had deep dyspareunia and rectal bleeding.⁸ A gynaecological examination revealed a tender, fixed retro-cervical nodule.⁸ An MRI was used to show a poorly defined, heterogenous mass, which seemed to invade the sigmoid colon.⁸ A colonoscopy was also performed showing a sessile luminal lesion.⁸ A slightly contrasting diagnostic process was used in a case of DIE of the colon, where the patient presented with intermittent rectal bleeding and dyschezia.⁵ The rectal bleeding had occurred with abdominal pain, on day 1–2 of her periods, over the last 2 years.⁵ An abdominal CT showed an asymmetrical thickening of the sigmoid colon, which was later confirmed to be DIE with histochemistry.⁵

The treatment of deep infiltrating sciatic nerve endometriosis is laparoscopic resection.² Medical therapy can be used to treat pain, but surgical intervention is needed once gait disorders and foot drop are involved.² With the development of laparoscopic surgery, the risks of infection, visceral injury and severe haemorrhages undertaken with an open approach can be mitigated.²

Endocrine therapy may be used in DIE, both as an adjuvant or as treatment for recurrences.⁹ With DIE especially, a complete resection can only be achieved in some cases; hence, the use of adjuvant endocrine therapy is often considered.⁹ Therapeutic options include oral contraceptives, gonadotropin-releasing hormone (GnRH) analogues and progestogens.^{9 10}

Oral contraceptives result in a pseudopregnancy state, that is, they suppress menses.⁹ Combined oral contraceptives downregulate cell proliferation and enhance apoptosis in the endometrium.¹⁰ The use of oral contraceptives remains a topic of debate, however, as it is speculated that previous use of contraception for primary dysmenorrhea may be a risk factor for endometriosis and DIE.¹⁰ In our case, patient declined this mode of treatment due to her further conception plan.

GnRH analogues effectively place women in a state of ‘artificial menopause’.¹⁰ This occurs through its inhibition of pituitary luteinising hormone, leading to a decline in oestradiol concentration.¹⁰ This should result in a loss of the menstrual period during treatment.¹⁰ A study of post treatment with GnRH analogues showed a temporary improvement in pain in patients with an incomplete surgical treatment.¹¹ However, the study found that this therapy did not have an effect on postsurgical pain in patients who had their DIE implants completely excised.¹¹ Our patient refused this treatment option in fear of the potential pharmacological side effects.

Dienogest is a progestogen dedicated for treating endometriosis.¹⁰ This medication works by suppressing the production of oestradiol, which impedes the growth of the endometrium.¹⁰ Dienogest can reduce the pain associated with endometriosis, with an efficacy comparable to GnRH analogues.¹⁰ An open label trial of daily dienogest showed a significant reduction in the severity of endometriosis, observed on laparoscopic examination.¹² Our patient would consider this option when she completes her family.

Finally, another important aspect of the long-term management of DIE to consider is the possibility of recurrence.¹³ DIE has been associated with a higher recurrence rate than other types of endometriosis.¹³ One study of 1106 endometriosis patients demonstrated a recurrence rate of 30.6% for DIE, compared with 17.8% in pelvic endometriosis, over a 4-year follow-up period.¹³ The rate of recurrence is increased with an incomplete excision.¹³ The administration of postoperative GnRH analogues in these patients has been shown to reduce symptoms; however, it is ineffective in improving the recurrence rate.¹³ It is a challenging discussion in terms of recurrent prevention in our case as the patient declined most of evident-based medical treatment for her conception and concern of side effects. We are continuing our clinical follow-up with assistance for her conception plan.

Patient’s perspective.

I was initially concerned about the pain and the possibility of a spinal canal problem or even cancer. The severity of the pain experienced was also quite disturbing, compromising my usual level of function. I was relieved and surprised when I was told about the final diagnosis. Overall, I was quite satisfied with the outcomes of the treatment and would like to continue to work with rehabilitation doctor to make a full recovery from the residual left ankle weakness.

Learning points.

• Menstrual relationship to the symptoms is a key finding and should be elucidated in patients with suspected endometriosis.

• The gold standard of treatment of deep infiltrative endometriosis of the sciatic nerve is a laparoscopic nerve resection. Complete eradication, however, is difficult to achieve.

• A long-term follow-up of patients is important due to the possibility of a recurrence. Adjuvant hormonal therapy can be used, but it may have unwanted side effects.

Ethics statements

Patient consent for publication

Obtained.