Background: Kennedy’s disease or spinal and bulbar muscular atrophy is an X-linked condition caused by a trinucleotide repeat expansion of a CAG repeat in the first exon of the androgen receptor gene. This mutation leads to an increased number of glutamine residues in the amino-terminal domain of the receptor. Androgen receptors are expressed widely in the brain and anterior horn cells of the spinal cord. It is hypothesized that the presence of these abnormal receptors is toxic to motor neurons which results in progressive bulbar and extremity muscle weakness. The androgen receptor mutation also results in partial androgen insensitivity. There are no specific therapies for Kennedy’s disease, but 5-alpha-reductase inhibitors which block the conversion of testosterone to the more potent dihydrotestosterone (DHT) have been reported to possibly lead to functional improvement.
Case Description: A 69-year-old man with a fifteen-year history of Kennedy’s disease functionally affected by swallowing difficulties, speech impairment and weakness of proximal arms and legs began treatment with 5-alpha-reductase inhibitor Dutasteride. He also had manifestations of androgen insensitivity with gynaecomastia and decreased sexual function. Prior to commencement of Dutasteride, his total testosterone level was 23.9nmol/L (6.0 - 28.0nmol/L), SHBG 75nmol/L (15-50nmol/L) and DHT 0.1nmol/L (0.4 – 2.5nmol/L). His creatine kinase was 256U/L (<201U/L). Following two years of treatment with Dutasteride, total testosterone was 22.6nmol/L (6.0 - 28.0mmol/L, DHT <0.1nmol/L (0.4 - 2.5nmol/L) and CK 380U/L (<201U/L). Subjectively, the patient reported improvement in his proximal upper and lower limb muscle strength but no change to his hypoandrogenism symptoms.
Summary: We report the case of a patient with Kennedy’s disease treated with 5-alpha-reductase inhibitor therapy. Total testosterone levels remained in the normal male reference range but with minor reduction of DHT levels. There was some subjective improvement in motor neuron symptoms but no change to manifestations of androgen insensitivity.