Kennedy's Disease (Spinal and Bulbar Muscular Atrophy)
Overview and Diagnosis
Kennedy's disease is a rare X-linked progressive neuromuscular disorder caused by CAG repeat expansion (>37 repeats) in the androgen receptor gene, characterized by lower motor neuron loss, muscle weakness, and bulbar dysfunction that manifests primarily in males. 1, 2
Key Diagnostic Features
- Progressive limb and bulbar muscle weakness with fasciculations and atrophy 1, 3
- Muscle cramps and tremors as common early symptoms 4
- Partial androgen insensitivity (gynecomastia, reduced fertility) distinguishes it from ALS 3
- Sensory neuronopathy on electrophysiological studies differentiates from pure motor neuron diseases 3, 4
- Slow progression compared to ALS, with relatively spared central nervous system pathways 3
Diagnostic Workup
- Genetic testing for CAG repeat expansion in the androgen receptor gene is confirmatory 1, 2
- Electrophysiological studies demonstrate both motor neuron and sensory nerve involvement 3, 4
- Neurofilament light (NfL) levels may be elevated and correlate with peripheral neuropathy severity 4
Management Strategy
Core Therapeutic Approach
Physical therapy should focus on submaximal, functional, and aerobic exercise while strictly avoiding excessive resistive and eccentric exercise to prevent overwork weakness. 5
Exercise Prescription
- Implement gentle strengthening within physiological limits with adequate rest periods between sessions 5
- Avoid high-intensity resistance training and eccentric exercises that can accelerate muscle damage 5
- Prioritize functional activities that maintain activities of daily living 5
Critical Pitfall: Muscle pathology occurs before motor neuron degeneration in SBMA, making muscle-targeted interventions particularly important early in disease course 6
Multidisciplinary Monitoring Schedule
Conduct comprehensive assessments every 6 months with the following team members 5:
- Neurology for disease progression monitoring
- Rehabilitation medicine for functional assessment
- Speech therapy for bulbar dysfunction (dysarthria, dysphagia)
- Nutrition for weight management and swallowing safety
Specific Interventions
Contracture Prevention
- Regular stretching programs to maintain range of motion 5
- Positioning strategies during rest and sleep 5
- Orthotic devices as needed for joint support 5
Functional Support
- Adaptive devices and assistive technology should be introduced proactively as weakness progresses 5
- Environmental modifications to maintain independence 5
Psychosocial Management
Designate a care coordinator to serve as the primary point of contact, providing continuity and navigation through the healthcare system 5
Mental Health Screening
- Screen for depression and anxiety at each visit, as these are common in chronic progressive neuromuscular diseases 5
- Provide psychological support for emotional adjustment and coping with progressive disability 5
- Facilitate connections with patient advocacy organizations and support groups 5
Genetic Counseling
Provide comprehensive genetic counseling for affected individuals and at-risk family members, emphasizing X-linked inheritance pattern and implications for male offspring 3
Current Treatment Limitations
There is currently no disease-modifying treatment or cure for Kennedy's disease. 3 Clinical care focuses on accurate diagnosis, symptom management, patient education, and genetic counseling 3. The androgen-dependent nature of the disease has prompted investigation of anti-androgen therapies, but no proven effective treatments exist 2.
Prognosis
Kennedy's disease is slowly progressive with disability accumulating over years to decades 1, 3. The rate of progression is significantly slower than ALS, and life expectancy may be near normal in many cases 3. Early muscle dysfunction precedes motor neuron loss, suggesting a window for muscle-targeted therapeutic interventions 6.