To investigate the efficacy of transdermal dihydrotestosterone therapy on 22 patients with microphallus, we applied dihydrotestosterone gel for 8 weeks to the external genitalia at daily doses of 12.5 mg. and 25 mg. for ages less than and older than 10 years, respectively. All patients were evaluated for penile and prostatic growth, pituitary-gonadal axis function, serum sex hormone binding globulin, lipid metabolism, hepatotoxicity, bone age and height velocity. All patients demonstrated growth of the penis during treatment. The mean increase rate (153%) in the first 4 weeks of treatment was higher than that (118%) of the second 4 weeks. Of importance is that responses were noted in 4 patients who had failed testosterone therapy for microphallus. The pituitary-gonadal axis was transiently suppressed during treatment, and serum sex hormone binding globulin and lipid metabolism were transiently affected during treatment. Serum alkaline phosphatase increased, mainly due to change of bone isoenzyme but bone ages and mean height velocity were not significantly affected. In conclusion, transdermal dihydrotestosterone therapy is an effective and relatively safe modality in the treatment of microphallus.
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