neurologic disorders
Weakness
Key Points
Distinguish loss of muscle strength from a feeling of fatigue. If fatigue has no anatomic or temporal pattern of weakness in patients with a normal physical examination, suspect chronic fatigue syndrome, an as-yet undiscovered systemic illness (eg, severe anemia, hypothyroidism, Addison disease), a psychologic problem (eg, depression), or an adverse medication effect. If patients have true muscle weakness, first focus on determining whether weakness is caused by dysfunction of the brain, spinal cord, plexuses, peripheral nerves, neuromuscular junction, or muscles. If patients have hyperreflexia and increased muscle tone (spasticity), particularly if Babinski reflex is present, suspect an upper motor neuron (eg, corticospinal tract) lesion in the brain or spinal cord; MRI is usually required. If patients have hyporeflexia, decreased muscle tone, muscle atrophy, and muscle fasciculations, suspect a lower motor neuron lesion. If patients have hyporeflexia and predominantly distal muscle weakness, particularly with distal sensory deficits or paresthesias, suspect polyneuropathy. If patients have difficulty climbing stairs, combing hair, and standing up with predominantly proximal muscle weakness and intact sensation, suspect myopathy. Physical therapy is usually helpful in improving strength for all causes of weakness. 