Insulin edema in slowly progressive type 1 diabetes: improvement following adjustment of insulin therapy

Insulin edema is an uncommon complication that typically arises soon after initiating insulin therapy, most often in individuals with newly diagnosed diabetes or poorly controlled hyperglycemia. An old report from a single hospital in Africa showed an incidence of 3.5% among 491 insulin-treated individuals. Although the precise pathophysiology remains uncertain, proposed mechanisms include insulin-induced sodium retention, increased vascular permeability, and dysregulation of the renin–angiotensin–aldosterone system. Insulin edema has been described in both type 1 and type 2 diabetes; however, occurrence in slowly progressive type 1 diabetes mellitus (SPIDDM) is exceptionally rare. We report a woman with SPIDDM who developed bilateral lower-leg edema shortly after starting basal–bolus insulin therapy with insulin aspart and insulin degludec. She exhibited no signs of heart failure, liver disease, renal impairment, or allergic reaction to insulin. Cardiac function was normal on echocardiography, and B-type natriuretic peptide levels were within the reference range. She experienced marked edema and an approximately 7-kg weight gain after insulin initiation. Following modification of the insulin regimen and dietary sodium restriction (8 g/day of salt), the edema resolved rapidly within nine days without the use of diuretics. This case illustrates that insulin edema can occur even in individuals with SPIDDM. The observed improvement after insulin regimen adjustment likely reflects the combined influence of glycemic stabilization, fluid–electrolyte balance, and potential formulation-related factors, rather than a direct causal difference between insulin types. Clinicians should recognize this rare yet clinically important complication and adopt an individualized management approach that includes careful glycemic correction and, when appropriate, adjustment of the insulin regimen.