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CHAPTER 18
Inflammatory Myopathies
Donald S. Younger, Marinos C. Dalakas
Inflammatory myopathy (IM) comprises three major and features. Affected patients present with subacute proximal
distinct subsets including polymyositis (PM), dermato- muscle weakness and myalgia that develops subacutely,
myositis (DM), sporadic and hereditary inclusion body usually over weeks to months, and progresses steadily, with-
myositis (sIBM and hIBM); and the related disorder necro- out evidence of a rash, extraocular or facial muscle involve-
tizing autoimmune myopathy (NAM), which is considered ment, or history of similarly affected family member.
in greater detail elsewhere (1–3). Although the presence
of moderate to severe muscle weakness and endomysial PM can be viewed as a syndrome of diverse etiology that
inflammation are common features in all these conditions, occurs separately or in association with systemic autoim-
respectively unique clinical, immunopathologic, and histo- mune and systemic collagen vascular disorders, and certain
logic criteria along with different prognosis and response to parasitic, viral, retroviral, and bacterial infections. There
therapies characterize each subset. This chapter reviews the may be a causal relation to concomitant toxic conditions
main clinical and histologic features of these diseases, their and myotoxic drugs causing myopathic symptoms such
association with autoimmune conditions or viruses, and as myalgia, often with transient or sustained elevation of
the underlying immunopathology. It also provides a practi- serum creatine kinase (CK) levels that typically improves
cal approach to immunotherapeutic interventions. with discontinuation of the offending agent but does not
lead to frank polymyositis.
CLINICAL DISORDERS
Examples of drug-induced, typically non-IM, cat-
Polymyositis egorized under the rubric toxic myopathies (1, 11)
Although first recorded by Wagner in 1863 (4), and named include NAM and rhabomyolysis due to statins, fibrates,
in the quarter century between 1954 and 1975, the distinc- ?-aminocaproic acid, and alcohol; mitochondrial myopa-
tive clinical, electromyogaphic, serum muscle enzyme fea- thy resulting from exposure to zidovudine, elevudine, and
tures, and histopathological aspects of PM and DM were statin medications; lysosomal and autophagic myopathy
described by Eaton (5), Walton and Adams (6), Rowland and neuromyopathy due to amiodarone and perihexiline;
(7), Pearson and Rose (8), Rose and Walton (9), and Bohan microtubular myopathy and neuromyopathy due to expo-
and Peter (10), distinguishing it from progressive muscular sure to vincristine; emetine-induced myofibrilar myopa-
dystrophy, and establishing the association with collagen thy, and acute quadriplegia myopathy.
vascular disorders.
With the exception of D-penicillamine, long-term, high-
The actual onset of PM cannot be easily determined. dose use of the antimalarial medications chloroquine and
Unlike in DM, in which the rash secures early recognition, hydroxychloroquine, the anti-gout medication colchicine,
patients with PM do not have unique heralding clinical interferon-? employed in the treatment of chronic active
hepatitis, cyclosporine and tarolimus used to prevent solid
organ transplant rejection, chronic administration of pred-
nisone in doses greater than 20 mg daily, and long term use
of the nucleoside analogue reverse transcriptase inhibitor
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