The idiopathic inflammatory myopathies (IIMs), including dermatomyositis (DM), polymyositis (PM), and inclusion body myositis (IBM), are characterized by proximal weakness and inflammation observed in the biopsy specimens of affected muscles (myopathy is an abnormal muscle condition; myositis is muscle inflammation). The main symptoms—weakness, fatigue, and muscle pain—are common complaints in primary care medicine that involve a diverse differential diagnosis with extensive overlap.
DM and PM are autoimmune diseases, and the symptoms often overlap with those of other autoimmune diseases, such as scleroderma, rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE). In addition, muscle inflammation may be seen on muscle biopsy specimens with viral, bacterial, and parasitic infections; sarcoidosis; eosinophilic myositis and macrophagic myofasciitis; and some muscular dystrophies.
Accurate diagnosis is essential for early and aggressive initiation of immunosuppressive therapy. In most cases, a physician may distinguish among the myopathies with a careful history and physical examination, combined with appropriate diagnostic testing. Once a diagnosis has been made, however, numerous issues arise about the disease and the medications used in treatment. Many complex issues may become active simultaneously, creating the risk that less active issues are neglected.
Close collaboration between the primary care physician and the physician who is managing the IIM is critical to the patient's overall care and well-being. In this article, I discuss the issues that often arise in IIM diagnosis and management and how physicians can address them with improved interaction with colleagues and patients.
Clinically, a patient with an IIM almost always presents with muscle weakness, usually with elevated muscle enzyme levels (eg, creatine phosphokinase [CPK]) and sometimes with myalgia (muscle pain). However, most patients with these complaints probably do not have an IIM because many patients who have other entities present with one or all of the symptoms; IIM is rare (incidence, about 1 case per 100,000 persons),1 and millions of patients are now taking lipid-lowering agents that may cause a toxic myopathy.2 Distinguishing DM and PM from other forms of myopathy is important, however, because these IIMs can be managed successfully with aggressive immunosuppressive therapy.
APPROACH TO PATIENTS WITH WEAKNESS OR FATIGUE
Is the patient weak?
Patients may have difficulty distinguishing weakness and fatigue, as well as asthenia (a feeling of exhaustion or a lack of energy in the absence of muscle weakness).3,4 Asthenia may be associated with excessive sleepiness, difficulty in concentrating, and depression; many patients refer to it as fatigue, but a decreased ability of a muscle to perform repetitive tasks is fatigability. In contrast, weakness is a reduction in the power of a muscle (eg, decreased ability to perform a task on the first try).
These 3 features may be confused easily, especially because they may occur in combination. For example, asthenia is a common feature of many autoimmune conditions (eg, RA and scleroderma) that is thought to be a consequence of the patient's inflammatory burden. If a patient with an autoimmune condition complains of increased weakness or fatigue, this complaint could represent a flare of the underlying illness, an evolution into an inflammatory myopathy, an adverse effect of a medication (eg, corticosteroids causing myopathy), or worsening depression associated with the chronic illness.
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