Key Takeaways 
A 40-year-old woman with type 1 diabetes mellitus (T1DM) who injected insulin into her abdomen developed a firm subcutaneous mass in the right lower quadrant. Pathology after surgical excision showed nodular cutaneous amyloidosis; mass spectrometry supported insulin injection-associated amyloid.

A case report by endocrinologist Meiying Zhuang, MD, and colleagues at Vancouver General Hospital, Canada, documents an underdiagnosed complication of repeated subcutaneous insulin injections.

The Patient and Her History
  The patient was referred to Vancouver General Hospital for a newly developed subcutaneous mass in the right lower abdominal quadrant, occasional night sweats, chills, paraesthesia’s migrating between her face and extremities, and intermittent arthralgias in the ankles, knees, hips, and wrists. She denied fever, unintentional weight loss, cough, chest pain, rashes, or gastrointestinal complaints.

Past medical history was notable for foetal alcohol syndrome and T1DM diagnosed at age 5 years.

Her regular medication was insulin, administered by subcutaneous injections into the abdomen for T1DM.

Family, social, substance use, travel, and allergy histories were unremarkable.

At the referring physician’s office, a biopsy of the lesion, measuring 1.1 × 1 × 0.8 cm, had been performed. Histology showed features of amyloidosis with strong Congo red staining.

Evaluation 
On admission, vital signs were within normal limits, including respiratory and heart rates,blood pressure, room air oxygen saturation, and body temperature.

Inspection, auscultation, palpation, and percussion corroborated the history. The biopsy wound in the right lower abdominal quadrant appeared noninflamed and dry. A firm, nonmobile mass was palpable beneath it. Additional findings included leg oedema and mild, nonspecific motor and sensory deficits in both lower legs.

A neurologic examination, including cerebrospinal fluid analysis, revealed no abnormalities.

An expanded amyloidosis workup — including complete blood count, electrolytes, creatinine, liver function tests, serum free light chains, serum protein electrophoresis, urine protein electrophoresis, and urinalysis — yielded no definitive clues.

A CT scan of the chest, abdomen, and pelvis showed a soft-tissue collection in the subcutaneous fat along the right anterior abdominal wall. No intrathoracic or intra- abdominal pathology was observed.

Echocardiography showed no evidence of amyloid deposition.

A repeat neurologic examination provided no new information.

Diagnosis and Management  After referral to the surgical department, the abdominal mass was excised. Subsequent histopathology revealed nodular cutaneous amyloidosis.

Given the patient’s frequent abdominal insulin injections, insulin injection-associated amyloidosis was considered in the differential diagnosis.