Acquired Ectopic Posterior Pituitary Bright Spot Due to Vasculotoxic Snakebite

ABSTRACT Objective Vasculotoxic envenomation is an uncommon cause of hypopituitarism. Most described cases have varying extent of anterior pituitary dysfunction, but posterior pituitary involvement is extremely rare. Methods Clinical, biochemical, and radiologic evaluation of a young female who presented with secondary amenorrhea was performed. A brief literature review of envenomation-induced hypopituitarism is included. Results A 26-year-old female presented with secondary amenorrhea since the age of 20 years. She had normal stature. Her past medical history was significant for a vasculotoxic snakebite 12 years back requiring hemodialysis, but no hormonal testing was done at that time. Current evaluation showed anterior hypopituitarism. An insulin-induced hypoglycemia test confirmed deficiencies of cortisol and growth hormone axes (peak values 348 nmol/L and 0.03 ng/mL). There was no diabetes insipidus. Magnetic resonance imaging revealed a hypoplastic anterior pituitary with an ectopic posterior pituitary. In view of normal stature and secondary amenorrhea, a diagnosis of envenomation-induced hypopituitarism with ectopic posterior pituitary (EPP) was made. A brief literature review of envenomation-induced hypopituitarism showed both acute and delayed presentation, male predominance, and variable lag period (weeks to years). Nearly half of all patients were asymptomatic. The most common axis involved in acute presentation was the cortisol axis, whereas the thyroid and gonadotroph axes were commonly involved in delayed hypopituitarism. Conclusion Vasculotoxic envenomation is a rare cause of acquired hypopituitarism. EPP in the index case was probably due to the “axonal dieback” phenomenon and subsequent regeneration of the axons at a more caudal site. This case, being the first instance of acquired EPP following envenomation, expands the spectrum of envenomation-induced hypopituitarism. Abbreviations EPP ectopic posterior pituitary HRT hormone replacement therapy