[57-year-old patient with diplopia and headache].

A 57-year old patient presented with an 8 week history of headache and diplopia. Left-sided incomplete oculomotor nerve paresis was found, whereas further clinically relevant visual impairment was not seen. Magnetic resonance imaging of the head showed an extensive intra-, para- and suprasellar tumor which in combination with a markedly elevated serum prolactin level was identified as a macroprolactinoma. The symptoms began 7 years ago with a loss of libido and virility. The application of a dopamine agonist lead to a reduction of serum prolactin level to 0.5% of the initial value and a considerable tumor regression within three months. The development of oculomotor nerve paresis is an unusual manifestation of prolactinoma. By contrast, long-term medical history with slowly developing signs and symptoms of hypogonadotropic hypogonadism are often to be found in men. The delayed diagnosis is responsible for the high percentage of macroprolactinomas in male subjects.