Male prolactinomas presenting with normal testosterone levels

Abstract

In men harboring prolactinoma the most common symptoms are related to hypogonadism, including decreased libido, erectile dysfunction, and gynecomastia. These men characteristically present with elevated serum prolactin (PRL) levels, suppressed gonadotropins, and low testosterone levels. We studied a group of 11 unique men with prolactinomas presenting with testosterone levels within the normal range (≥2.6 ng/ml; cohort A), and compared them to 11 prolactinoma men with borderline baseline testosterone (2.1–2.5 ng/ml; cohort B) and to a cohort of 34 prolactinoma patients with low testosterone levels (≤2 ng/ml; cohort C). Mean testosterone levels at presentation were 3.91 ± 0.9 ng/ml in cohort A (range, 2.6–5.2 ng/ml), 2.44 ± 0.16 ng/ml in cohort B and 0.96 ± 0.6 in cohort C (p < 0.001). Mean baseline PRL levels were >20 times above normal in cohort A compared to >100 times above normal in cohorts B and C. Symptoms of hypogonadism were present in 55, 64 and 76 % of men in groups A, B and C, respectively. There was a trend towards a larger tumor size in the low testosterone group (p = 0.06). Visual fields defects at presentation were more prevalent in this cohort (C). With cabergoline, testosterone level increased from 3.91 to 6.42 ng/ml (Δ = 2.51 ng/ml) in cohort A, from 2.44 to 5.63 ng/ml (Δ = 3.19 ng/ml) in cohort B, and from 0.96 to 3.30 ng/ml (Δ = 2.34 ng/ml) in cohort C (p < 0.05 for each group). Symptoms of hypogonadism improved following treatment in 83 % of symptomatic men in cohort A. Normal testosterone does not exclude the likelihood of prolactinoma in men. When treated with cabergoline, testosterone levels in these men can increase higher within the normal range together with clinical improvement.