Overview of KD and Diagnostic Considerations
About Kennedy’s Disease
Kennedy’s Disease (KD), also known as Spinal Bulbar Muscular Atrophy (SBMA), is a rare, X-linked, slowly progressive neuromuscular disorder that primarily affects men. The disease affects individuals differently, and severity and progression can vary widely. Symptoms often begin between the ages 30 and 50, although onset can occur anytime between 18 and 60.
While initially thought to affect 1 in 40,000, it is now thought that as many as 1 in 7,000 men are estimated to have the gene mutation that causes KD.
Females who inherit the gene mutation are considered carriers and have a 50% chance of passing the gene on to their children. Carriers may themselves experience some milder symptoms.
KD is often underdiagnosed or misdiagnosed as ALS (Amyotrophic Lateral Sclerosis), SMA (Spinal Muscular Atrophy), FSHD (Facioscapulohumeral Muscular Dystrophy), or other neuromuscular disease. Diagnosis is confirmed by genetic testing.
Diagnostic Considerations
Many patients first present to primary care with nonspecific symptoms such as muscle cramps, tremor, weakness, or gynecomastia. Early recognition and referral for neuromuscular evaluation improve patient support and reduce diagnostic delay.
Typical KD presentation includes:
- Slowly progressive proximal and bulbar weakness
- Fasciculations (can be global but characteristically perioral)
- Muscle cramps and tremor
- Dysphagia, dysarthria
- Androgen insensitivity signs (gynecomastia, reduced fertility)
- Metabolic abnormalities (insulin resistance, dyslipidemia)
Confirmed Diagnosis
- Definitive KD diagnosis requires genetic testing confirming Androgen Receptor CAG repeat expansion ≥38 repeats
- Family history consistent with X-linked inheritance is common
- CK is typically elevated
- EMG/NCS may show characteristic findings like fibrillation potentials, fasciculations, and large, polyphasic motor unit potentials, as well as sensory neuropathy
All patients with confirmed KD should be offered genetic counseling. Family members, particularly women of child-bearing age, may benefit from counseling regarding carrier status and reproductive options.
