Motor Neuron Disease Diagnosis and Management

Clinical Presentation

Upper motor neuron lesions produce spasticity, hyperreflexia, clonus, and extensor plantar responses, while lower motor neuron lesions cause flaccid paralysis, hyporeflexia/areflexia, fasciculations, and progressive muscle atrophy 1
Fasciculations are the most characteristic and likely sign following LMN damage, appearing as spontaneous discharges of entire motor units 2
Flaccid paralysis with decreased muscle tone and weakness is a common presentation of LMN lesions 1, 2
Hyporeflexia or areflexia with diminished or absent deep tendon reflexes is often seen in LMN disease 1, 2
Progressive muscle weakness and atrophy due to denervation is a hallmark of LMN lesions 1
Spasticity with increased muscle tone and velocity-dependent resistance is a characteristic of UMN lesions 1, 2
Hyperreflexia manifesting as brisk or exaggerated deep tendon reflexes is often seen in UMN disease 1, 2
Clonus showing rhythmic muscle contractions in response to sudden, maintained stretch is a sign of UMN lesions 1, 2
Extensor plantar response (Babinski sign) is a characteristic of UMN lesions 1

Electrodiagnostic studies, including EMG and nerve conduction studies, are mandatory for LMN confirmation 1
EMG findings in LMN disease include fibrillation potentials, positive sharp waves, fasciculations, and complex repetitive discharges indicating denervation 1
Nerve conduction studies in LMN disease show normal or low compound muscle action potential (CMAP) amplitudes with relatively normal conduction velocities 1
MRI brain without IV contrast is the optimal initial imaging modality for suspected motor neuron disease 1, 5
UMN findings on MRI include abnormal T2/FLAIR signal in the corticospinal tracts, particularly in the posterior limb of the internal capsule and cerebral peduncles 1, 5
LMN findings on spine MRI may show abnormal T2/STIR signal in the anterior horns ("snake eyes" appearance) 1, 5
Creatine phosphokinase (CK) should be measured when LMN involvement with weakness is identified 1
Thyroid function tests and electrolytes should be considered to exclude metabolic causes 2

Multidisciplinary care, including neurology, pulmonology, nutrition, physical therapy, occupational therapy, speech-language pathology, social work, and palliative care, improves survival and quality of life in motor neuron diseases 1, 5
Non-invasive ventilation (NIV) for respiratory insufficiency improves median survival and quality of life 1, 5
High suspicion for infections should be maintained in patients with LMN disease, as they are at high risk for pneumonia and respiratory failure 1
For SLE myelopathy with UMN signs, high-dose glucocorticoids combined with intravenous cyclophosphamide should be initiated within hours for optimal outcomes 1
For genetic forms of LMN disease, submaximal, functional, and aerobic exercise should be recommended while avoiding excessive resistive and eccentric exercise 1