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  • Updated 08.29.2024
  • Released 09.09.2019
  • Expires For CME 08.29.2027

Myositis and cancer

Introduction

Overview

There is a well-recognized association between cancer and myositis, mainly seen in classic dermatomyositis, amyopathic dermatomyositis, and immune-mediated necrotizing myopathy.

Idiopathic inflammatory myopathies, referred to as “myositis,” can be associated with cancer. Classic dermatomyositis, amyopathic dermatomyositis, and, to a lesser extent, polymyositis are the most highly affected myositis phenotypes, whereas immune-mediated necrotizing myopathy has been linked to cancer as a paraneoplastic phenomenon. Cancer-associated myositis is defined as the concomitant presence of the two diseases within a 3-year period. However, a paraneoplastic pattern—that is, when cancer abates, myositis disappears, and when malignancy recurs, myositis returns—is not always observed.

Key points

• The myositis phenotype most often associated with cancer is dermatomyositis.

• The temporal criterion (cancer and myositis diagnosed within 3 years) is mandatory for the diagnosis of cancer-associated myositis.

• International guidelines for idiopathic inflammatory myopathy-associated cancer screening have been established.

• The outcome of cancer-associated myositis depends more on the cancer than on the myositis.

• Close collaboration between the myositis-treating physician and oncologist is essential for optimal management of patients with cancer-associated myositis.

Historical note and terminology

Idiopathic inflammatory myopathies, generally referred to as myositis, are a heterogeneous group of systemic diseases, likely of autoimmune origin and characterized by an inflammatory infiltrate in muscle specimens (08). Five myositis phenotypes are recognized (30): dermatomyositis, which, when muscle symptoms are absent, is called amyopathic dermatomyositis; polymyositis, considered a rare condition and an exclusion diagnosis; necrotizing myopathy, which is mainly immune-mediated; sporadic inclusion body myositis; and overlap myositis, which includes the antisynthetase syndrome, manifesting as myositis, interstitial lung disease, and arthritis, among other features.

Myositis was first described in the late 19th century (19), and its association with malignancy was reported some years later (19). In the first classification of inflammatory myopathies (03), the authors established the criteria for polymyositis and dermatomyositis and recognized that an association between cancer and myositis was clearly found in some patients, mainly those with dermatomyositis. Well-conducted epidemiological studies found that dermatomyositis is the myositis phenotype most often associated with cancer, with polymyositis involved to a lesser extent (35; 04; 16). Unfortunately, studies focused on other myositis phenotypes are scarce and often of poor quality. A few observational or cohort studies have reported a higher risk of cancer relative to the general population in patients with immune-mediated necrotizing myopathy, particularly those without autoantibodies, and a weaker association in those with antibodies against 3-hydroxy-3-methylglutaryl coenzyme A (anti-HMGCR) (02). However, these data have not been replicated by others (34; 25).

Recommendations advocate taking into consideration the period between the two conditions to establish an association. A period of 3 years is now generally accepted; that is, cancer occurring within 3 years of the myositis diagnosis (38).

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