Dermatomyositis: an overview of recent progress with emphasis on dermatologic aspects☆

History

A historical perspective of the cutaneous manifestations of DM with special emphasis on C-ADM has recently been presented elsewhere by the author [14]. Keil [15] was among the first to accept the concept that patients can express the classic cutaneous manifestations of DM for years without the appearance of symptomatic muscle disease. The term amyopathic dermatomyositis seems to have been initially coined in 1979, not by a dermatologist but rather by a highly regarded rheumatologist and

Definitions and nomenclature

The IIM are a heterogeneous group of genetically determined autoimmune disorders that predominately target the skin and skeletal musculature resulting in widespread, highly symptomatic cutaneous inflammatory disease and limb girdle muscle weakness. In a relatively small percentage of patients, other organ systems, such as the lungs (eg, interstitial lung disease), joints (arthritis), and heart (eg, cardiomyopathy and conduction defects) can also be the target of inflammatory injury. On very

Classification

Because of the large differential diagnosis of proximal muscle weakness, modern rheumatologists, influenced by the earlier work of Bohan et al [33], [34], are very reticent to make a diagnosis of IIM in an adult without there being very firm evidence that this inflammatory myositis exists as the cause of weakness. This approach, however, often results in undervaluing the clinical specificity of the hallmark cutaneous manifestations of DM. Because of this specificity, the only significant

Risk of other systemic disease manifestations

DM can impact a number of organ systems beyond the skeletal muscles and skin, including lungs, joints, heart, gastrointestinal tract, and eyes. The most recent focus of interest in this area within the literature has been on pulmonary and joint disease.

Differential diagnosis

The contrasting features of the classic cutaneous manifestations of LE and DM have recently been emphasized with outstanding color illustrations [122]. In addition, the broad differential diagnosis of proximal muscle weakness has also been reviewed [7]. One curious report indicated that skin metastasis from breast cancer appeared clinically undistinguished from the skin involvement of amyopathic dermatomyositis [123].

Treatment

Oral or intravenous pulse corticosteroids remain the treatment of choice for suppressing all manifestations of newly diagnosed adult- and juvenile-onset classic DM patients. Methotrexate, cyclosporine, and high-dose intravenous immunoglobulin (IVIG) have traditionally been used as steroid-sparing agents. Similar benefit from mycophenolate mofetil has also been reported [124]. Cyclophosphamide is often used for difficult problems related to vasculitis-vasculopathy in childhood-onset disease.

Prognosis

A recent examination of prognosis in 77 consecutive patients with DM-PM having a minimum of 18 months follow-up revealed a 22% mortality rate resulting predominately from malignancy and lung disease [130]. As has been previously observed in both juvenile- and adult-onset classic DM, a better prognosis was seen in this study in individuals who received early systemic treatment for their disease. Poor outcome was associated with older age, pulmonary and esophageal involvement, and malignancy.

Etiology and pathogenesis

Fig. 3 presents a summary overview of current thinking concerning the etiology and pathogenesis of tissue injury (skin, muscle, lung, and so forth) in idiopathic inflammatory dermatomyopathies. Like other systemic autoimmune diseases involving autoantibody production, such as SLE, DM-PM is thought to evolve through multiple sequential phases: the susceptibility phase, the induction phase, the expansion phase, and the injury phase. A comprehensive discussion of this sequence of susceptibilities

Summary

Important points regarding DM and C-ADM are as follows:

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  C-ADM is a working functional designation for patients having the skin-only and skin-predominant subsets of DM, amyopathic DM, and hypomyopathic DM.

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  C-ADM seems to have approximately 10% the incidence of classic DM in whites and possibly a higher incidence in Asians.

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  Some patients who present with C-ADM, with or without subclinical laboratory abnormalities, can slowly progress to develop symptomatic muscle weakness over a period of years,

Acknowledgements

Dr. Sontheimer holds the John S. Strauss Endowed Chair in Dermatology at the University of University of Iowa College of Medicine/ Iowa Hospitals and Clinics (University of Iowa Health Care). The author thanks Dr Melissa Costner for her helpful thoughts and suggestions concerning this manuscript.