Insulin-Derived Cutaneous Amyloidosis: A Possible Complication of Repeated Insulin Injections

Abstract

Primary localized cutaneous amyloidosis (PLCA) is characterized by extracellular deposition of pathological fibril aggregation of proteins in the skin without systemic involvement. Macular amyloidosis, lichen (papular) amyloidosis, and nodular amyloidosis are three different subtypes of PLCA. Although the pathological mechanism of PLCA has not yet been clarified, it is assumed that a nucleus formation of amyloid fibril is formed due to repeated external stimulation, such as subcutaneous injection, which often poses diagnostic challenges. Herein, we present a 54-year-old Korean male patient with cutaneous localized amyloidosis which occurred after repeated local insulin injections, and discuss the relationship between insulin therapy in patients with diabetes mellitus and dermal amyloid deposition.

INTRODUCTION

Primary localized cutaneous amyloidosis (PLCA) is characterized by an extracellular deposition of pathological fibril aggregation of proteins in the skin without systemic involvement. Macular amyloidosis, lichen (papular) amyloidosis, and nodular amyloidosis are three different subtypes of PLCA. Despite many case reports over decades, the deposition of amyloids into the human tissues has not yet been fully understood¹,²,³,⁴,⁵. Insulin and enfuvirtide are known to be causative agents of cutaneous localized amyloidosis (LA)³,⁶.

Insulin-derived localized amyloidosis (IDLA), which was first reported in 1983, is a rare cutaneous complication of insulin injection in patients with diabetes mellitus (DM)⁷. Several case reports have been published describing patients with amyloid masses at insulin injection sites that were immunereactive to insulin antibodies², although reports of IDLA were rare in Korean literature. We experienced a case of pathologically-confirmed IDLA, and report a review of the literature.

CASE REPORT

A 54-year-old Korean male with type 2 DM noticed movable subcutaneous masses in both inner thighs, where insulin glargine (Lantus^®, Sanofi-Aventis) 36 units/ml had been regularly injected for 4 years (Fig. 1A, B). He had a history of hypertension and type 2 DM for more than a decade. The patient stated that he had injected 36 units of insulin glargine on his lower abdomen at first, and changed the injection sites to the inner thighs due to the occurrence of tender abdominal lumps. However, bilateral lumps occurred on both inner thighs where insulin was repeatedly injected.

Fig. 1. Clinical images of the affected areas. (A) An asymptomatic, well-defined, 5-cm sized, subcutaneous mass on the right inner thigh and (B) a 10-cm sized mass on the left inner thigh. (C) Preoperative magnetic resonance image showed enhancement of an ill-defined streaky lesion (yellow arrows) in the anterior fat layers of the left medial thigh.

Laboratory tests showed no particular abnormalities except elevated fasting glucose (264 mg/dl). A pelvic MRI with contrast revealed an enhancing, ill-defined mass around the nearly 3 cm-deep layer of fat on the left thigh (Fig. 1C). Near-total excision of the mass on the left thigh was performed under the suspicion for subcutaneous lipoma or injection granuloma. Histopathological findings showed extracellular deposition of eosinophilic amorphous material in the reticular dermis, localized foreign body reactions, and mild inflammatory cell infiltration. Several foreign body-type multinucleated giant cells were also observed (Fig. 2A). To exclude infectious disease, sarcoma, and cutaneous lymphoma, p16 protein was examined, and the stromal cells showed weak positivity (Fig. 2B). Congo red staining revealed apple-green birefringence amyloid depositions under a polarizing microscope, which strongly implicated IDLA (Fig. 2C, D).

Fig. 2. (A) There were scattered deposits of eosinophilic amorphous materials with partly foreign body reaction (H&E, ×200). (B) The result of immunohistochemistry with p16 protein showed a few positive stromal cells (p16, ×200). (C) Congo red positively stained on the amyloid materials (Congo red, ×200). (D) Polarizing microscopy revealed birefringent apple-green amyloid deposits in the lesion (polarizing microscopy, ×200).

After the complete resection of the mass on the patient’s left inner thigh, the lump on the right side spontaneously regressed with the cessation of insulin injection, and the patient could not find any palpable mass.

We received the patient’s consent form about publishing all photographic materials.

DISCUSSION

The typical appearance of IDLA consists of firm subcutaneous nodules at the sites of insulin injection of DM patients (29.9%~44.4%), and only few reports regarding LA exist to date²,⁸.

The pathological mechanism has not yet been clarified, but it is assumed that a nucleus formation of amyloid fibril is formed due to repeated external stimulation, such as subcutaneous injections¹,⁹. One possible hypothesis is the absence of the C-peptide in iatrogenic recombinant insulin¹⁰,¹¹. Natural human proinsulin is composed of an A-chain and a B-chain that are connected by the C-peptide. A previous study showed that the C-peptide can interfere with insulin fibril formation. Pathologically, chronic active inflammatory changes as well as foreign body reaction with multinucleated giant cells are often seen in IDLA. Direct cytotoxicity to cells of the organs has also been demonstrated, and perturbation of insulin degradation enzyme may play a role, damaging the injected insulin and making it biologically inactive¹¹,¹².

Several mechanisms by which amyloid deposits prevent the absorption of injected insulin have been proposed, including one that states insulin may not be able to penetrate the lesion to reach the effective dose. The literature also demonstrated that patients with IDLA showed well-controlled hemoglobin A1c levels after resection, or by alternating the injection sites⁹. Characteristics of previously reported cases on drug-induced localized amyloidosis are summarized in Table 1¹³,¹⁴,¹⁵,¹⁶,¹⁷,¹⁸,¹⁹.

Table 1. Summary of clinical and histopathologic features of drug-induced and insulin-derived localized amyloidosis in the literatures.

Author	Sex/age (yr)	Location	Duration	Causative agent	Diagnostic tools	Treatment
Störkel et al. (1983)7	N/A	N/A	6 wk	Insulin (porcine)	Congo red, IHC	Surgical excision
Dische et al. (1988)13	M/25	Thigh	4 yr	Insulin (porcine, isophane)	Congo red, IHC, non-branching amyloid fibrils (EM)	Surgical excision
Swift et al. (2002)4	M/34	Thigh	17 yr	Insulin	Congo red, human insulin antibody, non-branching amyloid fibrils (EM)	Surgical excision
Sahoo et al. (2003)14	M/54	Shoulder	N/A	Insulin	Congo red, Diff-Quick stain	Surgical excision
Albert et al. (2007)15	M/59	Abdomen	12 yr	Insulin (isophane, lispro)	Congo red	Surgical excision
Morilla et al. (2009)16	M/47	Arm	N/A	Enfuvirtide*	Congo red	Surgical excision
Lonsdale-Eccles et al. (2009)17	M/40	Arm	N/A	Insulin (humulin)	Congo red,human insulin antibody, non-branching amyloid fibrils (EM)	Surgical excision
Yumlu et al. (2009)3	M/33	Arm	10 yr	Insulin (regular, aspart, isophane, glargine, detemir)	Congo red	Surgical excision
	F/78	Abdomen	4 yr	Insulin (regular, isophane)	Congo red	Surgical excision
	F/42	N/A	N/A	Insulin (regular, isophane, aspart)	Congo red	Surgical excision
	M/38	Arm	N/A	Insulin (isophane, lispro)	Congo red	Surgical excision
Shikama et al. (2010)1	F/60	Abdomen	16 yr	Insulin (humulin, aspart, detemir)	Congo red	Surgical excision
Endo et al. (2010)18	F/70	Abdomen	N/A	Insulin	Congo red, human insulin antibody	N/A
Nagase et al. (2014)2	M/62	Abdomen	20 yr	Insulin (glargine, lispro)	Congo red	N/A
Hagiwara et al. (2017)19	M/62	Abdomen	20 yr	Insulin (glargine, lispro)	Congo red	Surgical excision
Samlaska et al. (2020)12	M/61	Leg, arm, abdomen	N/A	Insulin (glargine, aspart, lispro)	Congo red	Surgical excision
Our case	M/54	Thigh and abdomen	4 yr	Insulin (glargine)	Congo red	Surgical excision

N/A: not available, IHC: immunohistochemistry, M: male, F: female, EM: electron microscope. ^*Enfuvirtide: anti-retroviral drug, used in treatment of HIV infection.

Diagnostic tests for IDLA involves thorough skin examinations, laboratory tests, and skin biopsy. A specimen often shows strong affinity for Congo red stain, which is frequently used as a specific marker of amyloid fibrils, although the dye is also capable of binding to some other proteins such as albumin and cellulose²⁰. The presence of non-branching fibrils (7.5 to 10 nm in diameter) on electron microscopy, and a positive result by immunostaining for insulin autoantibodies are also confirmative diagnostic tools. There are only few reports that describe the radiological manifestations of subcutaneous amyloidosis⁸. In the present case, an ill-defined mass that invaded a 3 cm-deep layer of the subcutaneous fat was observed on pelvic bone MRI.

For the differential diagnosis of LA, lipohypertrophy due to the fat-increasing effect of insulin should be excluded. Although both lesions have a common feature of decreased insulin absorption, in the case of lipohypertrophy, the effect of the lesion on blood glucose control is limited. On the other hand, the absorption is strongly decreased in the amyloid-containing lesions of LA, leading to critically impaired blood glycemic control⁸. Also, unlike LA, lipohypertrophy usually regress with the cessation of insulin injection. Another distinctive feature of LA is that the lesions are more solid and firm. Nodular amyloidosis, subcutaneous lipoma, and liposarcoma should be differentiated as well, when a subcutaneous lump occurs with insulin injection into large muscles like inner thighs or abdomen.

It is often impossible to completely cease subcutaneous insulin injection in patients with DM, therefore, surgical excision and alternating the injection sites are recommended for the treatment. The mainstay in the treatment of LA often remains supportive therapy. Conservative management should be considered to reduce the supply of the proteins that are the precursors of the amyloid deposition.

Identifying IDLA is important because poor glycemic control and higher requirements of insulin are related severe complications. Evaluating insulin lispro or insulin aspart, several studies revealed that insulin absorption is profoundly impaired at IDLA sites². The difference in the incidence of IDLA in long-acting insulin versus short-acting insulin is unclear, but most patients were administered more than 36 units of short, intermediate, and long-acting insulin combination therapy for a long-term period.

In conclusion, we experienced a rare case of IDLA, and the patient exhibits no signs of worsening or recurrence of the lesion. When patients with type 2 DM who present with a mass at an insulin injection site, the occurrence of IDLA as an adverse event of exogenous insulin should be routinely investigated in etiological clinical studies.