Endocrine Abstracts

A 48-year man, referred with symptoms suggestive of phaeochromocytoma and elevated 24 h urinary noradrenalin level. He had a background history of obstructive sleep apnoea, controlled hypertension and obesity. His medications included Amlodipine 10 mg od, Modafinil 200 mg daily, Amitriptyline 10 mg and Rabeprazole.

Obstructive sleep apnoea was diagnosed at 39 years. CPAP was tried and later Modafinil 100 mg daily. A few months prior to referral his Modafinil was increased to 200 mg daily.

Systemic examination was unremarkable. Anterior pituitary function tests, U&E, bone profile, LFT, CRP were normal. Urinary catecholamine measured off Modafinil was normal while a rechallenge on Modafinil 200 mg showed elevated noradrenalin levels. Urinary metanephrines & CT scan of the adrenals were normal.

Modafinil acts by blocking the reuptake of noradrenalin by the noradrenergic terminals in hypothalamus. Some studies have shown increased heart rate & bloodpressure whilst on modafinil. In our case on a modest dose of 200 mg of modafinil, patient was symptomatic. The elevated 24 h urinary catecholamines suggest significant adrenomedullary activation by Modafinil rather than a phaeochromocytoma.