Physical diagnostic clues of conditions that can cause muscle weakness
| Condition | Key features | Effect on reflexes | Clinical findings |
|---|---|---|---|
| Leptomeningeal disease | Multilevel neuraxial nerve roots involved, leading to asymmetric weakness | May have hyperreflexia with eventual loss of reflexes due to ongoing compression of nerve roots | With or without radicular pain |
| Cauda equina | Asymmetric weakness caused by 2 or more nerve roots (L2–sacrum, lumbosacral nerve roots) | May have hyperreflexia early, which ultimately leads to loss of tone and areflexia | Gradual, unilateral onset Saddle numbness (S3–S5) with or without lower-extremity sensory deficits |
| Conus medullaris | Symmetric weakness with prominent sphincter dysfunction and flaccid bladder and rectum paralysis (L1–L2; sacral cord segment and roots) | Less marked hyperreflexia at ankles with distal paresis and fasciculation | Sudden, bilateral onset Mixed upper motor neuron and lower motor neuron signs Perianal numbness with or without sexual deficits or impotence Leg weakness is mild |
| Horner syndrome | Ipsilateral eyelid ptosis | Miosis on swinging light test | Anhidrosis from ipsilateral sympathetic nerve injury |
| Neurogenic thoracic outlet syndrome | Intrinsic hand muscle atrophy with or without grip weakness or finger abduction | May be diminished due to muscle atrophy | With or without upper-extremity sensory deficits May have positive Spurling testa Consider Adson maneuverb to ensure arterial sufficiency and Pemberton signc to rule out superior vena cava compression |
| Polyneuropathy | Multifocal and asymmetric distribution | Decreased deep tendon reflexes | Paresthesia and pain that can be followed by ataxia Decreased sensation Consider testing for anti-Hu, anti-CRMP5, and antiamphiphysin antibodies |
↵aPosition the head of the seated patient by extending the neck, rotating it to the affected side, and tilting the head to the same side. The test is positive if applying downward pressure on the top of the head elicits radicular pain.
↵bRadial pulse is lost when the patient rotates their head to the affected side and takes a deep breath.
↵cThe patient lifts both arms overhead with forearms touching the side of the face for about 1 minute and the clinician observes for any of the following positive signs: facial congestion, cyanosis, or respiratory distress.
Based on information from reference 27.