3.4. Motor Neuron Disease Associated with Physical Agents
Electrical Injury
- General considerations:
- Causes a delayed upper and lower motor neuron syndrome after both electrical injury or lightening
- Starts at the site of trauma and then spreads
- Transient weakness and paraplegia following electrical injury which usually clears after hours to 4 days
- Permanent sequelae occurs with symptoms starting with years after the accident
- The pathology is not the same as autopsies of executed criminals
- Clinical features:
- The source of the current is usually from household circuits, high voltage lines or lightening (usually causes severe burns and cardiac arrest)
- Electrical current specifically travels down the corticospinal and bladder pathways
- Weakness and atrophy often begins at the site of injury
- Weakness spreads in a contralateral pattern
- Bulbar signs and upper motor neuron weakness and spasticity occur over time
- Chronic regional pain syndrome (CRPS) frequently occurs with its motor manifestations of:
- Inability to initiate movement
- Tremor
- Spasticity
- Weakness
- Atrophy are often concurrent
- Death often occurs within three years in some patients
Post Radiation Motor Neuron Syndrome
- General considerations:
- Delayed occurrence after X-RT
- Dosages to the cervical spine that cause the syndrome are: approximately 3000 rads; lumbosacral spine 5000–6000 rads
- Associated with treatment of many different types of tumors
- Clinical features:
- Occurs months to years after treatment
- Atrophy of affected muscles with fasciculations
- No sphincter involvement
- Normal sensation
- Lower extremities are preferentially involved
- Weakness usually stabilizes, but has been described to progress over years
- A similar process occurs in the lower cranial nerves with head and neck irradiation. The carotid artery is often involved in this situation with a long segment of the artery involved and consequent stroke
- EMG evaluation:
- Fibrillation potentials are present in the lower extremities
- Myokymic discharges occur
- Laboratory evaluation:
- CSF usually normal
- Protein may be slightly elevated
Differential Diagnosis
The myokymic potentials in the lower extremities and usual lack of involvement of the upper extremities make the diagnosis. Tumor recurrence does occur on this background. This is particularly important with sarcomas of the brachial plexus after X-RT of the breast. The same problem occurs following X-RT involvement for a variety of brachial plexus conditions.
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