is a decrease in muscle strength or power; weakness
is also a general term commonly used by patients to describe a state of low energy. Neurologic weakness may be a focal symptom, involving a single muscle group, or it may be generalized. A chief complaint of weakness requires a systematic history and physical to develop a working differential diagnosis and to direct testing. Clarification of what the patient means by “weakness” and a distinction between low energy versus diffuse motor weakness versus focal motor weakness is the starting point of the evaluation. The emergency department (ED) approach takes into account the possible, and at times rare, life-threatening causes including stroke, spinal cord lesions, toxic exposures, metabolic abnormalities, botulism, myasthenia gravis, and Guillain-Barré syndrome (GBS), among others. In evaluating weakness, the clinician must always consider disorders that can precipitously compromise the respiratory and functional status of the patient; see Chapter 7: Myopathies and Neuromuscular Junction Disorders
for a more detailed evaluation of respiratory decompensation.
A key first step is differentiating loss of neuromuscular power from the sensation of generalized weakness. This may be complicated by the fact that presentations are not strictly binary; for example, hypothyroidism may present with general fatigue plus a myopathy. The history begins with elucidating the location of the complaint and whether it is symmetrical, focal, or generalized; other features include the acuity of onset and duration of symptoms, exacerbating and mitigating factors, and presence of associated symptoms.
Because neuromuscular weakness is the inability to perform a desired movement with normal force and power due to a reduction in muscle strength and function, these patients are likely to complain of an inability to perform specific tasks. Asking open-ended questions such as “what activities can you no longer do?” may be a good place to start with a patient having difficulty explaining their weakness in detail. Also, asking task-specific questions such as “are you having any difficulty brushing teeth, combing hair, rising from a chair, walking upstairs, opening a jar or door, etc.” can be helpful primers to jump-start the dialogue for the patient. Patients who are unable to respond to questions about specific tasks and give more generalized histories of weakness are more likely to have a non-neuromuscular etiology.
Sudden onset of weakness suggests a vascular catastrophe, such as a spinal cord hemorrhage, and requires emergent evaluation. A slower progression of symptoms may suggest a metabolic disorder such as hyperkalemia, or disorders such as GBS or myasthenia gravis. A history of symmetric ascending weakness in a patient with a recent respiratory illness will aid in the diagnosis of GBS. The weakness of myasthenia gravis may fluctuate, and a careful history is needed to elicit a progression of symptoms throughout the day or an association with exercise, temperature extremes, such as hot showers, or repeated activity, such as chewing or combing one’s hair.
Recent illness, other medical problems, occupational history, travel history, history of tick bites, use of medications, and use of recreational drugs are all important factors to assess in the patient complaining of weakness. A thorough review of systems includes inquiry about recent weight loss, fever or sweats, visual changes (including diplopia), difficulty swallowing, joint or muscle pain, palpitations, change in bowel habits, and skin rashes. Occupational or recreational exposures may indicate drug toxicity.
The physical examination begins with a full set of vital signs including oxygen saturation and a finger blood glucose. A blood glucose level should be obtained early during the evaluation, as hypoglycemia may present with an array of symptoms, including weakness. Capnometry may be useful in identifying and monitoring patients with weakness associated with compromised ventilation and is supplemented with obtaining a forced vital capacity or negative inspiratory force measurements. Tachycardia, with or without hypotension, suggests volume depletion including anemia, or toxic drug ingestion. Rectal temperature measurement is particularly important in that
infections frequently present with nonspecific complaints, such as weakness. The ears, sinuses, thyroid, and cardiac status should be assessed, as well as a careful evaluation for signs of trauma, which may suggest physical abuse.
TABLE 4.2 Motor Strength Grading System (Medical Research Council Scale)
Active movement against gravity and resistance
Active movement against gravity (no resistance from physician)
Active movement with gravity eliminated (no resistance from physician)
Flicker or trace contraction
No visible or palpable contraction
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