Motor Neuron Disease, Degenerative

Key Features

Essentials of Diagnosis

• Weakness and wasting of muscles

• No sensory loss or sphincter disturbance

• Progressive course

• No identifiable underlying cause other than genetic basis in familial cases

• Cigarette smoking may be a risk factor

General Considerations

• There is degeneration of the

  • Anterior horn cells in the spinal cord

  • Motor nuclei of the lower cranial nerves

  • Corticospinal and corticobulbar pathways

• Five varieties have been characterized on clinical grounds

PROGRESSIVE BULBAR PALSY

• Bulbar involvement predominates

• Disease processes affect primarily the motor nuclei of the cranial nerves

PSEUDOBULBAR PALSY

• Bulbar involvement predominates

• Due to bilateral corticobulbar disease and thus reflects upper motor neuron dysfunction

PROGRESSIVE SPINAL MUSCULAR ATROPHY

• A lower motor neuron deficit in the limbs

• Due to degeneration of the anterior horn cells in the spinal cord

PRIMARY LATERAL SCLEROSIS

• There is a purely upper motor neuron deficit in the limbs

AMYOTROPHIC LATERAL SCLEROSIS

• A mixed upper and lower motor neuron deficit is found in the limbs

• Approximately 10% of cases of amyotrophic lateral sclerosis are familial

• This disorder is sometimes associated with cognitive decline (in a pattern consistent with frontotemporal dementia), a pseudobulbar affect, or parkinsonism

Demographics

• Symptoms generally begin between 30 and 60 years of age

• The disease is usually sporadic, but familial cases may occur

Clinical Findings

Symptoms and Signs

• Difficulty in swallowing, chewing, coughing, breathing, and talking (dysarthria) occur with bulbar involvement

• In progressive bulbar palsy, there is

  • Drooping of the palate

  • A depressed gag reflex

  • Pooling of saliva in the pharynx

  • A weak cough

  • A wasted, fasciculating tongue

• In pseudobulbar palsy, the tongue is contracted and spastic and cannot be moved rapidly from side to side

• Limb involvement is characterized by motor disturbances (weakness, stiffness, wasting, fasciculations) reflecting lower or upper motor neuron dysfunction

• There are no objective changes on sensory examination, though there may be vague sensory complaints

• The sphincters are generally spared

Differential Diagnosis

UPPER MOTOR NEURON DISEASE

• Stroke

• Space-occupying lesion

• Compressive spinal cord lesion

• Multiple sclerosis

LOWER MOTOR NEURON DISEASE

• Infections of anterior horn cells (eg, poliovirus or West Nile virus)

• Radiculopathy, plexopathy, peripheral neuropathy, and myopathy are distinguished by clinical examination

• Pure motor syndromes resembling motor neuron disease may occur in association with

  • Monoclonal gammopathy

  • Multifocal motor neuropathies with conduction block, which can be distinguished by electrodiagnostic studies

• A motor neuronopathy may ...