Muscle Weakness in Adults: Evaluation and Differential Diagnosis

Scott T. Larson; Jason Wilbur

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Jan 15, 2020 Issue

Muscle Weakness in Adults: Evaluation and Differential Diagnosis

SCOTT T. LARSON, MD, and JASON WILBUR, MD, University of Iowa Carver College of Medicine, Iowa City, Iowa

Am Fam Physician. 2020 Jan 15;101(2):95-108.

Author disclosure: No relevant financial affiliations.

Although the prevalence of muscle weakness in the general population is uncertain, it occurs in about 5% of U.S. adults 60 years and older. Determining the cause of muscle weakness can be challenging. True muscle weakness must first be differentiated from subjective fatigue or pain-related motor impairment with normal motor strength. Muscle weakness should then be graded objectively using a formal tool such as the Medical Research Council Manual Muscle Testing scale. The differential diagnosis of true muscle weakness is extensive, including neurologic, rheumatologic, endocrine, genetic, medication- or toxin-related, and infectious etiologies. A stepwise approach to narrowing this differential diagnosis relies on the history and physical examination combined with knowledge of the potential etiologies. Frailty and sarcopenia are clinical syndromes occurring in older people that can present with generalized weakness. Asymmetric weakness is more common in neurologic conditions, whereas pain is more common in neuropathies or radiculopathies. Identifying abnormal findings, such as Chvostek sign, Babinski reflex, hoarse voice, and muscle atrophy, will narrow the possible diagnoses. Laboratory testing, including electrolyte, thyroid-stimulating hormone, and creatine kinase measurements, may also be helpful. Magnetic resonance imaging is indicated if there is concern for acute neurologic conditions, such as stroke or cauda equina syndrome, and may also guide muscle biopsy. Electromyography is indicated when certain diagnoses are being considered, such as amyotrophic lateral sclerosis, myasthenia gravis, neuropathy, and radiculopathy, and may also guide biopsy. If the etiology remains unclear, specialist consultation or muscle biopsy may be necessary to reach a diagnosis.

Given its broad differential diagnosis, muscle weakness can be challenging to evaluate in primary care practice. Although its prevalence in the general population is not well described, muscle weakness occurs in 5% of U.S. adults 60 years and older.1 Physicians must distinguish true muscle weakness from subjective fatigue or pain-related motor impairment with normal motor strength. This requires a history and physical examination, which guide laboratory testing, imaging, electrodiagnostic testing, and muscle biopsy.2–5

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SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation	Evidence rating	Comment
History and physical examination findings should guide laboratory testing, imaging, electromyography, and muscle biopsy in patients with muscle weakness.^2–5	C	Usual practice and expert opinion
A medication and toxin review should be completed in patients with muscle weakness.^4,12,15,35	C	Usual practice and expert opinion
Electromyography should be performed in patients with muscle weakness if the diagnosis is unclear after a history, physical examination, and targeted laboratory evaluation.^15,18,19,26	C	Expert opinion
Muscle biopsy should be considered to clarify the diagnosis in patients who have objective muscle weakness with elevated creatine kinase levels or abnormal findings on electromyography or muscle magnetic resonance imaging.^20,21	C	Expert opinion

A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to https://www.aafp.org/afpsort.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation	Evidence rating	Comment
History and physical examination findings should guide laboratory testing, imaging, electromyography, and muscle biopsy in patients with muscle weakness.^2–5	C	Usual practice and expert opinion
A medication and toxin review should be completed in patients with muscle weakness.^4,12,15,35	C	Usual practice and expert opinion
Electromyography should be performed in patients with muscle weakness if the diagnosis is unclear after a history, physical examination, and targeted laboratory evaluation.^15,18,19,26	C	Expert opinion
Muscle biopsy should be considered to clarify the diagnosis in patients who have objective muscle weakness with elevated creatine kinase levels or abnormal findings on electromyography or muscle magnetic resonance imaging.^20,21	C	Expert opinion

Etiology and Differential Diagnosis

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Abstract
Etiology and Differential Diagnosis
History
Physical Examination
Laboratory Evaluation
Imaging and Electrodiagnostic Testing
Muscle Biopsy
References

The differential diagnosis

The Authors

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SCOTT T. LARSON, MD, is a clinical assistant professor in the Department of Family Medicine at the University of Iowa Hospitals and Clinics, Iowa City....

JASON WILBUR, MD, is the director of the Geriatric Medicine Fellowship Program, associate director of the Family Medicine Residency Program, and a clinical professor in the Department of Family Medicine at the University of Iowa Carver College of Medicine, Iowa City.

Address correspondence to Jason Wilbur, MD, University of Iowa Carver College of Medicine, 200 Hawkins Dr., Iowa City, IA 52242 (email: jason-wilbur@uiowa.edu). Reprints are not available from the authors.

Author disclosure: No relevant financial affiliations.

References

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