Muscle weakness, not pain, is the hallmark feature of inflammatory myopathies. In polymyositis and dermatomyositis, the muscle weakness is typically proximal and symmetric. Inclusion body myositis can present with more distal end asymmetric muscle involvement.
Patients will typically present with various manifestations of muscle weakness such as difficulties walking, climbing stairs, getting up from a chair, or swallowing. The most concerning manifestation is respiratory muscle weakness with shortness of breath due to restrictive respiratory failure. Muscle pain is typically mild and present in about half of patients.
Patients with dermatomyositis may present with new or worsening skin findings, including Gottron papules, erythroderma, heliotrope erythema, shawl sign, or mechanic’s hands.
The vast majority of patients with active inflammatory myositis will have a profoundly elevated creatinine kinase. In inclusion body myositis, the creatinine kinase elevation may be less prominent.
Just as in other systemic rheumatic diseases, various organ- or life-threatening manifestations can be subclinical in these patients and do require a careful diagnostic evaluation. The most feared complications in inflammatory myositis involve the lungs. Patients can have various types of interstitial lung disease and profound respiratory muscle weakness. While renal involvement in inflammatory myositis is rare, it can be associated with other connective tissue disorders such as systemic lupus or scleroderma. Therefore, diagnostic testing should always include a urinalysis to detect glomerulonephritis.
Atrophic Dermal Papules of Dermatomyositis (ADPDM). Formerly Gottron papules, ADPDM are erythematous to purpuric, scaly, flat-topped papules on the dorsal metacarpophalangeal joints. Mechanic’s hands features (hyperkeratosis and scaling of ulnar side of the thumb and radial side of the index finger) are also seen. (Image appears with permission from VisualDx [www.visualdx.com].)
Dermatomyositis—Heliotrope Eruption. A violaceous, edematous periorbital erythema with mild scaling is considered pathognomonic for dermatomyositis. This patient with undiagnosed dermatomyositis presents with the periorbital swelling, myalgias, and elevated creatinine kinase. (Photo contributor: R. Jason Thurman, MD.)
Management and Disposition
Patients with respiratory failure either due to worsening interstitial lung disease or respiratory muscle weakness may require respiratory support such as bilevel positive airway pressure or intubation.
In cases of organ- or life-threatening manifestations such as severe pulmonary or renal involvement, immediate treatment was high-dose corticosteroids may be indicated. This should be done in close consultation with nephrology and rheumatology.
Dermatomyositis—Shawl Sign. Sunlight-exacerbated poikilodermatous or macular erythema of the upper back, neck, and posterior shoulders (“shawl sign”) or anterior neck and upper chest (“V sign”). (Photo contributor: Lawrence B. Stack, MD.)