Patients with acromegaly have characteristic clinical features of soft tissue overgrowth. Both somatic and metabolic features of acromegaly are secondary to excess GH secretion and high circulating levels of insulin-like growth factor 1 (IGF1). However, an acromegaloid phenotype associated with severe insulin resistance is occasionally seen in the absence of biochemical hallmarks of acromegaly (insulin-mediated pseudoacromegaly). Here we present a case of insulin-mediated pseudoacromegaly with an acromegaloid phenotype, insulin resistance, history of adenomatous colonic polyp, and suppressed IGF1 levels.
Patients with this rare condition are likely to have a selective post-receptor defect of insulin signalling. The insulin resistance in this condition may be secondary to impaired insulin-stimulated phosphatidylinositol (PI) 3-kinase activity. The hyperinsulinaemia occurring in compensation for the impaired metabolic signalling may activate intact mitogenic signalling pathways and stimulate pathological tissue growth. Endocrinologists should be aware of this diagnosis when assessing patients with clinical features of acromegaly and insulin resistance, in the absence of elevated levels of GH and IGF1.