Insulin induced tan: a dual diagnosis

We present the case of a young male patient diagnosed with type 1 diabetes whose skin noticeably darkened with insulin therapy. Minimal insulin requirements, an unexpectedly low HbA1c and ongoing symptoms of weight loss and anorexia prompted further investigations. He was found to have a suboptimal response to synthetic ACTH (Synacthen) confirming a diagnosis of Addison's disease (primary adrenal failure). We postulate that the lowering of the blood glucose with insulin therapy for type 1 diabetes unmasked the diagnosis of Addison's disease. The case highlights several important lessons: (1) beware the dual diagnosis – hypoglycaemia in diabetic patients may have another cause and other autoimmune diseases are more likely; (2) the interaction between separate pathologies may modify the behaviour of each disease; and (3) ensure steroid replacement is appropriate and the patient is aware of steroid precautions and the need for early intervention with illness. Copyright © 2015 John Wiley & Sons.