Concomitant occurrence of macroprolactin, exercise-induced amenorrhea, anda pituitary lesion: a diagnostic pitfall - Case report

The authors report the case of a 37-year-old woman who presented with ameno rrhea and an increased level of serum prolactin. Magnetic resonance images of the pituitary revealed a lesion with characteristics consistent with tho se of a microadenoma. Transsphenoidal exploration was performed, but a prol actinoma was not found. After endocrinological review, the patient's hyperp rolactinemia was found to be caused by the presence of macroprolactin and h er amenorrhea was due to intense exercise and low body weight. Macroprolact in is an isoform of prolactin that is variably reactive in assays for prola ctin, but displays minimum bioactivity in vivo. Patients with macroprolacti n are mostly asymptomatic. This phenomenon may cause elevated prolactin val ues, which the authors view as apparent hyperprolactinemia. The presence of macroprolactin is an underrecognized problem, occurring in as many as 15 t o 20% of patients with elevated prolactin values and often leading to unnec essary, expensive diagnostic procedures and inappropriate treatment. The pr esence of macroprolactin should always be suspected when the patient's clin ical history or clinical or radiological data are incompatible with the pro lactin value. Physicians dealing with diagnosis and treatment of hyperprola ctinemia (general practitioners, gynecologists, neurosurgeons, endocrinolog ists, and biochemists) should be aware of the potentially misleading nature of macroprolactin.