Causes of Anterior Horn Cell Disorders
Yes, motor neuron disease (MND), spinal muscular atrophy (SMA), poliomyelitis, and Kennedy's disease (spinal and bulbar muscular atrophy) are all correct causes of anterior horn cell disorders. 1
Classification of Anterior Horn Cell Disorders
Anterior horn cell disorders affect the cell bodies of lower motor neurons located in the anterior horn of the spinal cord, representing a central nervous system disorder with peripheral manifestations 1. These disorders are characterized by:
- Degeneration of motor neurons in the anterior horn of the spinal cord 1
- Clinical presentation with muscle weakness and atrophy 1
- Absence of sensory symptoms (unlike peripheral neuropathies) 1
- Characteristic EMG findings showing denervation with fibrillation potentials, positive sharp waves, and fasciculations 1
Specific Anterior Horn Cell Disorders
1. Motor Neuron Disease (MND)
- Most common type is amyotrophic lateral sclerosis (ALS), representing approximately 85% of all MND cases 2
- Characterized by degeneration of both upper and lower motor neurons in the brain and spinal cord 2
- Other variants include Progressive Muscular Atrophy (PMA) and Progressive Bulbar Palsy (PBP) 2
- MRI findings may include abnormal T2/STIR signal in the anterior horns ("snake eyes" appearance) 2, 3
2. Spinal Muscular Atrophy (SMA)
- Autosomal recessive neuromuscular disorder with degeneration of alpha motor neurons in the anterior horn cells 4
- Caused by homozygous loss of function of the survival motor neuron gene SMN1 on 5q13 4
- Incidence of approximately 1 in 10,000 live births, making it the second most common autosomal recessive disorder 4
- Clinical classification based on age of onset and maximum function achieved 5
- Recent therapeutic advances include nusinersen, onasemnogene abeparvovec, and risdiplam 4, 6
3. Poliomyelitis
- Viral infection that selectively destroys anterior horn cells 1
- Can lead to Post-Polio Syndrome, which develops 30-40 years after acute poliomyelitis in 25-40% of affected individuals 1
- Post-Polio Syndrome is characterized by new muscle weakness, pain, and exacerbation of existing weakness 1
4. Kennedy's Disease (Spinal and Bulbar Muscular Atrophy)
- X-linked recessive disorder affecting anterior horn cells 1, 7
- Characterized by slowly progressive multisystem disease with a motor neuron disease phenotype 7
- Features partial androgen insensitivity and electrophysiological evidence of sensory neuronopathy 7
- Can be differentiated from ALS by its slow progression and relatively spared central nervous system pathways 7
Diagnostic Approach
- Electrodiagnostic studies are crucial for differentiating anterior horn cell disorders from peripheral neuropathies 1
- MRI of the head without IV contrast is recommended as the initial imaging modality for suspected motor neuron disease 2, 3
- Genetic testing is important for specific diagnoses, particularly in SMA (SMN1 gene) and familial ALS 2, 4
Clinical Pitfalls and Considerations
- Anterior horn cell disorders must be distinguished from peripheral neuropathies, which typically present with both sensory and motor symptoms 1, 8
- Cervical spondylotic myelopathy can mimic anterior horn cell disorders but typically has upper motor neuron signs and sensory involvement 1
- Some immune-mediated disorders may present with predominantly lower motor neuron features and are important to recognize as they are potentially treatable 8
- Regular assessment of motor function is recommended at 3-6 month intervals for children under five years, and annually in older children and adults 1, 3