Bulbospinal muscular atrophy

Bulbospinal muscular atrophy (BSMA), also known as Kennedy disease or X-linked spinal and bulbar muscular atrophy (SBMA), is a rare neurodegenerative disorder caused by an expansion of a CAG trinucleotide repeat in the androgen receptor (AR) gene on the X chromosome. The disease primarily affects lower motor neurons in the spinal cord and brainstem (bulbar region), leading to progressive muscle weakness and atrophy. Because the condition is X-linked and androgen-dependent, it predominantly affects males, with females typically being carriers who may show mild or no symptoms. Key clinical features include slowly progressive proximal limb weakness, muscle wasting, fasciculations (visible muscle twitching), and bulbar symptoms such as difficulty swallowing (dysphagia), speech difficulties (dysarthria), and tongue atrophy with fasciculations. Patients frequently experience muscle cramps, tremor, and exercise intolerance. Androgen insensitivity signs are also characteristic, including gynecomastia (breast enlargement), testicular atrophy, reduced fertility, and erectile dysfunction. Sensory neuropathy may also be present. Elevated creatine kinase levels are commonly found on laboratory testing. The disease typically manifests in adulthood, usually between the ages of 30 and 50, though onset can vary. There is currently no cure or disease-modifying treatment for bulbospinal muscular atrophy. Management is supportive and multidisciplinary, focusing on physical therapy to maintain mobility, speech therapy for bulbar symptoms, nutritional support for swallowing difficulties, and monitoring for potential cardiac and metabolic complications such as glucose intolerance and hyperlipidemia. Research into androgen-lowering therapies and other molecular approaches is ongoing, though clinical trials have not yet yielded a proven effective treatment. Life expectancy is generally near normal, though bulbar dysfunction can lead to aspiration pneumonia, which is a significant cause of morbidity and mortality.

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