Panniculitis at the Site of Injection: Infection or Foreign Body Reaction?

Abstract

Abstract Introduction/Objective A 63 year old diabetic female presented to the dermatology clinic with painful abdominal nodules. The nodules seemed to wax and wane every 1–2 weeks and appeared in different locations on the abdomen. The lesions were subcutaneous, tender, firm, and mobile with no discoloration. The patient had diabetes treated with injectable exenatide but no other significant medical or travel history. Methods The differential diagnoses included mycobacterial infection, mechanical insult from injectable diabetes medication, erythema nodosum, erythema induratum, and lupus panniculitis. Ultrasound was indicative of panniculitis. A biopsy of the active lesion was performed. Results The biopsy showed septal and lobular panniculitis with mixed inflammation and multinucleated giant cells. Small, circular, non-polarizable pink amphorous material was associated with the infiltrate. The amphorous material was strongly acid fast. The patient had a negative quantiferon-TB test. Scanning electron microscopy with energy dispersive x-ray analysis showed that the material contained more oxygen and less carbon than surrounding tissue, but no abnormal elements were identified. Infrared spectroscopy of the foreign material most closely matched poly(L- lactide-co-glycolide). Conclusion The diagnosis of exenatide induced granulomatous panniculitis was made. The patient had recently started using this injectable glucagon-like peptide-1 receptor agonist, which has been associated with panniculitis. The injectable formulation is loaded onto microspheres composed of poly (DL-lactic-co-glycolic acid), which is closely related to poly(L-lactide-co-glycolide). This material has been shown to stain strongly acid fast. This case of granulomatous panniculitis due to injectable diabetic medication highlights an important potential pitfall that pathologists should be aware of, especially in cases where mycobacterial infection is in the differential.