All Is Swell: A Case Report of Insulin Edema Syndrome

Insulin edema syndrome is a rare and underrecognized complication of insulin initiation or intensification, characterized by peripheral or generalized edema. Its pathophysiology is multifactorial, involving renal salt retention, increased capillary permeability, and vasodilation, and it is often a diagnosis of exclusion. We report the case of a 41-year-old man with newly diagnosed type 2 diabetes mellitus presenting with hyperglycemia (772 mg/dL) and marked weight loss. After initiation of insulin glargine and lispro, he developed rapid-onset generalized edema, including scrotal and lower extremity swelling, weight gain of 32 pounds, dyspnea, and pleural effusions. An extensive workup excluded cardiac, renal, hepatic, infectious, autoimmune, and protein-losing enteropathy etiologies. The edema worsened with higher insulin doses despite treatment with diuretics and corticosteroids. Transition to NPH (neutral protamine Hagedorn) and regular insulin, with adjunct dapagliflozin, resulted in rapid resolution of the edema, allowing discontinuation of the diuretics. Risk factors for insulin edema include newly diagnosed diabetes, rapid glycemic correction, low body weight, and high insulin doses. While generally self-limiting, severe or refractory cases may require diuretics or modification of the insulin regimen. Recognition is critical to avoid unnecessary interventions and to manage symptoms effectively. Insulin edema syndrome should be considered in patients presenting with unexplained edema after insulin initiation. Dose adjustment or switching insulin analogs, combined with supportive management, can lead to rapid improvement. Awareness of this condition may help prevent misdiagnosis and unnecessary invasive procedures.