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An Approach to Myopathy for the Primary Care Clinician

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Patients with muscle weakness are frequently encountered in the primary care clinic; however, the identification of an underlying disorder of muscle can pose a significant challenge. The aim of this review article is to provide a clinical and diagnostic framework to aid the primary care clinician in the detection and evaluation of suspected myopathies.

Introduction

Myopathies are a heterogeneous collection of disorders characterized by the abnormal structure or functioning of skeletal muscle. Such disorders are frequently encountered in primary care practices; however, the recognition and diagnosis of these conditions can be challenging. In this review, we will discuss the symptoms and signs that may alert practitioners to the possibility of underlying muscle disease, as well as the basic elements of an appropriate diagnostic workup, and when to refer to a specialist.

Symptoms

As with most neurologic disorders, the diagnosis of myopathy begins with taking a careful and thorough history. Patients often report symptoms of fatigue, exercise intolerance, generalized weakness, and muscle pain; however, these symptoms are relatively nonspecific and may reflect nonmyopathic conditions, including cardiopulmonary disorders, orthopedic conditions, rheumatologic diseases, medication use, deconditioning, and even depression. In contrast, symptoms that should raise suspicions of an underlying myopathy include discrete patterns of muscle weakness, fatigable weakness, muscle atrophy, myotonia, and recurrent myoglobinuria.1

The evaluation of a patient with suspected myopathy should include a discussion of the duration of symptoms and history—including developmental and early childhood history—as well as a family history of similar symptoms or diagnosed myopathy. Certain congenital, metabolic, and mitochondrial myopathies may present at birth or in early childhood, with such issues as failure to thrive, delayed motor milestones, and contractures, whereas other hereditary and acquired myopathies may not present until adolescence or adulthood. Inflammatory myopathies such as polymyositis and dermatomyositis may occur at any age, whereas inclusion body myositis often presents in late adulthood.

A discussion regarding the tempo of symptom onset and progression, as well as any provoking or exacerbating factors, may also provide diagnostic clues when evaluating patients with presumed muscle disease. For example, patients reporting the onset of symptoms after the initiation of a lipid-lowering therapy may be experiencing an acquired medication-induced myopathy, whereas those with symptoms after a carbohydrate-rich meal may have a periodic paralysis. For patients who describe a family history of disease, one should attempt to determine an inheritance pattern, because this can help guide future genetic testing and counseling.

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-Rose M. Domingo-Horne, MD, Mohammad Kian Salajegheh, MD

This article originally appeared in the March issue of The American Journal of Medicine.

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