Kennedy’s Disease: Clinical Features of X-Linked Spinal and Bulbar Muscular Atrophy

X-linked Spinal and Bulbar Muscular Atrophy (SBMA), commonly known as Kennedy’s Disease, is a distinct adult-onset neurodegenerative disorder affecting adult males. Caused by a trinucleotide CAG repeat expansion in the first exon of the androgen receptor (AR) gene on the X chromosome, Kennedy's disease combines lower motor neuron degeneration with signs of partial androgen insensitivity.

Symptoms typically manifest between the third and fifth decades of life. Proximal limb weakness progresses slowly, often starting in the pelvic or shoulder girdles. Characteristic clinical markers include:

• Facial and Perioral Fasciculations: Present in over 90% of patients, these fasciculations are often elicited when patients blow out their cheeks or whistle.

• Endocrine Manifestations: Gynecomastia, testicular atrophy, and reduced fertility occur due to impaired androgen receptor function. A subset of patients may also develop type 2 diabetes mellitus.

• Electrodiagnostic Profile: Electromyography reveals widespread reinnervation changes with large-amplitude, long-duration polyphasic motor unit action potentials. Notably, sensory nerve action potentials (SNAPs) are characteristically absent or low in amplitude, reflecting underlying sensory neuronopathy despite minimal clinical sensory loss.

• Laboratory Findings: Marked elevation of serum creatine kinase (CK) is common, sometimes reaching levels up to 8,000 U/L.

Bulbar weakness, including dysarthria and dysphagia, typically develops late in the disease course. Because disease progression is slow, life expectancy is often normal or only slightly reduced.