A typical presentation of type B insulin resistance syndrome with isolated hypoglycaemia and suppressed insulin.

Type B insulin resistance syndrome is a rare autoimmune disorder affecting glucose homeostasis characterised by the presence of serum autoantibodies to the insulin receptor. Typically, these patients present with severe insulin resistance although a mixed hyperglycaemic and hypoglycaemic phenotype may also occur, as can an exceptionally rare isolated hypoglycaemia presentation. The classic biochemical pattern comprises elevated insulin levels despite significant hypoglycaemia. We report an adult man presenting with isolated hypoglycaemia and suppressed serum insulin and C-peptide levels. He demonstrated evidence of autoimmunity with positive antinuclear antibodies, reactive lymphadenopathy and cytopaenias but did not meet the criteria for systemic lupus erythematosus and underlying malignancy was not identified despite extensive investigation. Insulin receptor antibodies were present. Treatment with prednisone led to resolution of hypoglycaemia, with no recurrence after 36 months of follow-up. However, 42 months after initial presentation, he represented with high-grade lymphoma.