General
- Disuse of muscles
- Anemia
- Malnutrition
- Electrolyte abnormality, eg, hypercalcemia, hypokalemia, hyponatremia
- Endocrine disease, eg, hypothyroidism, diabetes mellitus, Cushing’s syndrome, Addison’s disease, hyperaldosteronism
- Chronic lung or heart disease
- Malingering
Upper motor neuron disease
- Stroke
- Space-occupying lesion, eg, brain tumor
- Spinal cord lesion
- Multiple sclerosis
Lower motor neuron disease
- Anterior horn cell, eg, poliomyelitis, amyotrophic lateral sclerosis (ALS), West Nile virus
- Motor nerve root, eg, disk protrusion
- Nerve plexus, eg, brachial plexus neuropathy
- Peripheral nerve, eg, diabetes mellitus, alcoholism, heavy metals, Guillain-Barré syndrome
- Neuromuscular junction, eg, myasthenia gravis, Eaton-Lambert syndrome, botulism, organophosphate poisoning, tick paralysis, drug-induced, eg, aminoglycoside
- Myopathy, eg, polymyositis, corticosteroids, hypothyroidism, alcohol
- Other: aortic dissection, periodic paralysis, eg, hypokalemic, hyperkalemic, thyrotoxic