Differential Diagnosis in Neurology

3.5. Rare Causes of Motor Neuron Disease

Hyperparathyroidism

• General considerations:
  • Several series and isolated case reports associate an ALS picture with hyperparathyroidism
  • Skepticism about the nature of the correlation persists due to lack of EMG correlation of wide spread denervation and failure to halt progression of the disease with removal of the parathyroid glands
• Clinical features:
  • Symmetrical proximal weakness with cramps
  • Hyperactive reflexes and spasticity
  • Inconsistent tongue fibrillations and dysphagia
  • Inconsistent sensory loss
  • Several patients had bladder urgency
• EMG evaluation:
  • Widespread denervation in some patients

Repeated Hypoglycemia

• General considerations:
  • The syndrome of anterior horn cell disease has occurred in patients with repeated episodes of hypoglycemia
• Clinical considerations:
  • Wasting of extremities
  • Fasciculations

Motor Neuron Disease with HIV/ HTLV-I

• General considerations:
  • HIV frequently causes a vacuolar cervical myelopathy; and severe axonal neuropathy
  • HTLV-I causes a severe chronically progressive cervical /thoracic myelopathy with spasticity and bladder involvement
• Clinical features:
  • A few patients with HIV present with ALS or a primary lateral sclerosis syndrome
  • Most patients have severe lower extremity spasticity and bladder involvement

Postpoliomyelitis Syndrome

• General considerations:
  • Approximately 500,000 Americans suffer from the diseases
  • Last great epidemic occurred in 1952
  • A few isolated cases have occurred from vaccination; most cases now occur from unvaccinated communities or immigrants
• Clinical features:
  • Further weakening of muscles that had previously been affected
  • Fasciculations in affected muscles
  • Fatigue
  • No upper motor neuron signs
  • Weakness of bulbar and respiratory muscles does occur
  • Patients who have survived polio often have fasciculation for a prolonged period in affected muscles

Drugs Associated with Motor Neuron Disease

Lead

• General considerations:
  • Most often encountered in battery workers, mechanics (car radiator repair)
  • Often associated with systemic signs of anemia, lead lines in gum and bone
  • Renal cortex involvement
  • Basophilic stippling of RBC
• Clinical features:
  • Lower motor involvement of wrist and finger extensors
  • One report of both upper and lower motor neuron involvement

Other Drugs causing Rare Forms

• Rare forms:
  • Dapsone
  • Nitrofurantoin may present with dose dependent reversible lower motor neuron syndrome
  • Guamanian ALS dementia complex has been linked to toxic amino acid ingestion from the cycad nut (Brn methylamine BNXAA). Now not thought to be etiologic