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Key Clinical Questions

  • image Is the onset of weakness abrupt/acute, gradual/subacute, or insidious/chronic?

  • image Is the weakness stable, progressively worsening, waxing and waning, or fatigable?

  • image Is the weakness symmetric or lateralized?

  • image Is the weakness length-dependent?

  • image Are the involved muscles all weak to the same degree?

  • image If a gradient of weakness exists, is it worse proximally or distally?

  • image Are specific muscles or groups of muscles weak?

  • image Do the involved muscles correspond to a myotome or a portion of the brachial or lumbar plexus?

  • image Are there nonmotor deficits?


  • The pace of onset of neurological symptoms, including weakness, is the best clue as to its etiology. Vascular events (ischemic and hemorrhage stroke) cause abrupt symptom onset, inflammatory and infectious symptoms tend to develop over hours to days, and symptoms resulting from neurodegeneration develop over weeks to years. There are, of course, exceptions.

  • Defining the pattern of weakness as well as the presence or absence of other associated symptoms is the key to accurate neuroanatomic localization. In a given patient, one lesion causing all symptoms is more likely than several lesions each causing a single symptom.


  • A major concern in a patient with progressive weakness is airway protection. Slurred speech, drooling, coughing, choking, a nasal or hoarse voice, weakness of neck flexion or extension, or gasping for air should alert the clinician to the possibility of neuromuscular airway compromise. The airway should be secured immediately.

  • Bedside testing of pulmonary function including vital capacity and negative inspiratory force measurements are helpful but are dependent on patient cooperation and effort and should not replace or overly reassure one’s clinical impression.

  • Neurological conditions in which the airway may be particularly susceptible include acute ischemic and hemorrhagic stroke, acute inflammatory demyelinating polyneuropathy (Guillain-Barré syndrome), amyotrophic lateral sclerosis (ALS), and diseases affecting the basilar meninges and the lower cranial nerves.

Weakness is a common neurological symptom that can result from dysfunction of many parts of the central and peripheral nervous system as well as from disorders of muscle itself. Familiarity with the anatomy of the motor system including the corticospinal tract and its peripheral projections, and the relationship of these pathways to nonmotor (sensory and autonomic) pathways, aids in the localization of neurological deficits.

The role of the clinician in the evaluation of a patient with weakness is to first establish the pace of onset and distribution of symptoms and then to formulate an anatomic localization of the lesion. Diagnostic testing including imaging and electrophysiologic examinations may follow, though these tests should always be hypothesis-driven so that the pretest probability of detecting a causative abnormality is increased, and the probability of detecting incidental and noncausative abnormalities is reduced.

The clinician should be mindful that patients may describe weakness as numbness, and vice versa. Furthermore, weakness is frequently reported as a symptom of fatigue, exhaustion, malaise, pain, or depression, all of which are not ...

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