Suspect myopathy? Take this approach to the work-up

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Applied Evidence

Suspect myopathy? Take this approach to the work-up

J Fam Pract. 2014 November;63(11):631-638

Brent W. Smith, MD

Jason C. McCarthy, MD

Courtney A. Dawley, DO

This practical guide, with handy reference tools, will help you to distinguish between myopathy and nonmyopathic disease and further refine your diagnosis.

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References

1. Huynh CN, Yanni LM, Morgan LA. Fibromyalgia: diagnosis and management for the primary healthcare provider. J Womens Health. 2008;8:1379-1387.

2. Crum-Cianflone NF. Bacterial, fungal, parasitic, and viral myositis. Clin Microbiol Rev. 2008;21:473-494.

3. Reichlin M, Arnett FC Jr. Multiplicity of antibodies in myositis sera. Arthritis Rheum. 1984;27:1150-1156.

4. Yoshino M, Suzuki S, Adachi K, et al. High incidence of acute myositis with type A influenza virus infection in the elderly. Intern Med. 2000;39:431-432.

5. Dalakas MC, Hohlfeld R. Polymyositis and dermatomyositis. Lancet. 2003;362:971-982.

6. Wilson FC, Ytterberg SR, St Sauver JL, et al. Epidemiology of sporadic inclusion body myositis and polymyositis in Olmsted County, Minnesota. J Rheumatol. 2008;35:445-447.

7. Smith EC, El-Gharbawy A, Koeberl DD. Metabolic myopathies: clinical features and diagnostic approach. Rheum Dis Clin N Am. 2011:37:201-217.

8. Reuters V, Teixeira Pde F, Vigário PS, et al. Functional capacity and muscular abnormalities in subclinical hypothyroidism. Am J Med Sci. 2009;338:259-263.

9. Nieman LK, Biller BM, Findling JW, et al. The diagnosis of Cushing’s syndrome: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2008;93:1526-1540.

10. Holick MF, Binkley NC, Bischoff-Ferrari HA, et al; Endocrine Society. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96:1911-1930.

11. Antons KA, Williams CD, Baker SK, et al. Clinical perspectives of statin-induced rhabdomyolysis. Am J Med. 2006;119:400-409.

 12. Phillips PS, Haas RH, Bannykh S, et al; Scripps Mercy Clinical Research Center. Statin-associated myopathy with normal creatine kinase levels. Ann Intern Med. 2002;137:581-585.

13. Pereira RM, Freire de Carvalho J. Glucocorticoid-induced myopathy. Joint Bone Spine. 2011;78:41-44. 

14. Posada C, García-Cruz A, García-Doval I, et al. Chloroquine-induced myopathy. Lupus. 2011;20:773-774.

 15. Uri DS, Biavis M. Colchicine neuromyopathy. J Clin Rheumatol. 1996;2:163-166.

 16. Mannix R, Tan ML, Wright R, et al. Acute pediatric rhabdomyolysis: causes and rates of renal failure. Pediatrics. 2006;118:2119-2125. 

17. Pozio E. World distribution of Trichinella spp. infections in animals and humans. Vet Parasitol. 2007;149:3-21. 

18. Rodolico C, Toscano A, Benvenga S, et al. Myopathy as the persistently isolated symptomatology of primary autoimmune hypothyroidism. Thyroid.1998;8:1033-1038. 

19. AACE/AAES Task Force on Primary Hyperparathyroidism. The American Association of Clinical Endocrinologists and The American Association of Endocrine Surgeons position statement on the diagnosis and management of primary hyperparathyroidism. Endocr Pract. 2005;11:49-54.

20. Garber JR, Cobin RH, Gharib H, et al; American Association of  Clinical Endocrinologists and American Thyroid Association Taskforce on Hypothyroidism in Adults. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocrine Pract. 2012;18:988-1028.

21. Bahn Chair RS, Burch HB, Cooper DS, et al; American Thyroid Association; American Association of Clinical Endocrinologists. Hyperthyroidism and other causes of thyrotoxicosis: management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists. Thyroid. 2011;21:593-646.

22. Mammen AL, Amato AA. Statin myopathy: a review of recent progress. Curr Opin Rheumatol. 2010;22:644-650.

23. Buettner C, Davis RB, Leveille SG, et al. Prevalence of musculoskeletal pain and statin use. J Gen Intern Med. 2008;23: 1182-1186.

24. Marot A, Morelle J, Chouinard VA, et al. Concomitant use of simvastatin and amiodarone resulting in severe rhabdomyolysis: a case report and review of the literature. Acta Clin Belg. 2011;66:134-136.

25. Peters BS, Winer J, Landon DN, et al. Mitochondrial myopathy associated with chronic zidovudine therapy in AIDS. Q J Med. 1993;86:5-15.

PRACTICE RECOMMENDATIONS

› Categorize patients with muscle complaints into suspected myositic, intrinsic, or toxic myopathy to help guide subsequent work-up. C
› Look for diffusely painful, swollen, or boggy-feeling muscles—as well as weakness and pain with exertion—in patients you suspect may have viral myopathy. C
› Consider electromyography and muscle biopsy for patients you suspect may have dermatomyositis. C

Strength of recommendation (SOR)

A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series

CASE › Marie C, a 75-year-old Asian woman, reports weakness in her legs and arms with unsteadiness when walking. She has a vague but persistent ache in her large muscles. Her symptoms have developed slowly over the past 3 months. She denies recent signs or symptoms of infection or other illness. Her medical history includes hypertension, hyperlipidemia, osteopenia, and obesity. Ms. C takes lisinopril 10 mg/d and atorvastatin, which was recently increased from 10 to 20 mg/d.

What would your next steps be in caring for this patient?

Patients who experience muscle-related symptoms such as pain, fatigue, or weakness often seek help from their family physician (FP). The list of possible causes of these complaints can be lengthy and vary greatly, from nonmyopathic conditions such as fibromyalgia to worrisome forms of myopathy such as inclusion body myositis or polymyositis. This article will help you to quickly identify which patients with muscle-related complaints should be evaluated for myopathy and what your work-up should include.

Myopathy or not?

Distinguishing between myopathy and nonmyopathic muscle pain or weakness is the first step in evaluating patients with muscle-related complaints. Many conditions share muscle-related symptoms, but actual muscle damage is not always present (eg, fibromyalgia, chronic pain, and chronic fatigue syndromes).¹ While there is some overlap in presentation between patients with myopathy and nonmyopathic conditions, there are important differences in symptoms, physical exam findings, and lab test results (TABLE 1^1-4). Notably, in myopathic disease, patients’ symptoms are usually progressive, vital signs are abnormal, and weakness is common, whereas patients with nonmyopathic disease typically have remitting and relapsing symptoms, normal vital signs, and no weakness.

Myopathy itself is divided into 3 categories—myositic, intrinsic, and toxic—which reflect the condition, or medication, that brought on the muscle damage (TABLE 2^2,4-15). Placing patients into one of these categories based on their risk factors, history, and physical exam findings can help to focus the diagnostic work-up on areas most likely to provide useful information.

Myositic myopathy can be caused by infection or autoimmunity

Myositic myopathies result in inflammatory destruction of muscle tissue. Patients with myositic myopathy often exhibit fever, malaise, weight loss, and general fatigue. Though weakness and pain are common, both can be variable or even absent in myositic myopathy.^2,5Myositic myopathy can be caused by infectious agents or can develop from an autoimmune disease.

Infectious myositic myopathy is one of the more common types of myopathy that FPs will encounter.²Viruses such as influenza, parainfluenza, coxsackievirus, human immunodeficiency virus, cytomegalovirus, echovirus, adenovirus, Epstein-Barr, and hepatitis C are common causes.^2,4,16Patients with  a viral myositis often report prodromal symptoms such as fever, upper respiratory illness, or GI distress one to 2 weeks before the onset of muscle complaints. Bacterial and fungal myositides are relatively rare. Both most often occur as the result of penetrating trauma or immunocompromise, and are generally not subtle.²Parasitic myopathy can occur from the invasion of skeletal muscle by trichinella after ingesting undercooked, infected meat.²Although previously a more common problem, currently only 10 to 20 cases of trichinellosis are reported in the United States each year.¹⁷Due to their rarity, bacterial, fungal, and parasitic myositides are not reviewed here.

Patients with a viral myositis often report prodromal symptoms such as fever, upper respiratory illness, or gastrointestinal distress one to 2 weeks before the onset of muscle complaints. Muscle pain is usually multifocal, involving larger, bilateral muscle groups, and may be associated with swelling.

Patients with viral myositis may exhibit diffusely painful, swollen, or boggy-feeling muscles as well as weakness and pain with exertion. Other signs of viral infection such as rash, fever, upper respiratory symptoms, or meningeal signs may be present. Severe signs include arrhythmia or respiratory failure due to cardiac muscle or diaphragm involvement, or signs of renal failure due to precipitation of myoglobin in the renal system (ie, rhabdomyolysis).²If the infection affects the heart, patients may develop palpitations, pleuritic chest pain, or shortness of breath.²

Diagnosis of viral myositis relies heavily on clinical suspicion in patients with a fitting history and physical exam findings. Helpful lab tests include a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), creatine kinase (CK), and liver function tests (LFTs), all of which can be abnormal in viral myositis. Viral polymerase chain reaction, culture, or antigen testing may be helpful in severe or confusing cases, but in most cases such testing is unnecessary. Muscle biopsy is not recommended except in persistent cases, where definitive identification of the causative agent might alter treatment or when nonviral infection is suspected.²