Symptoms of polymyositis and dermatomyositis

Symptoms of polymyositis and dermatomyositis

What are the clinical features of polymyositis (PM) and dermatomyositis (DM)? 

Although PM is an adult disease, DM occurs in both children and adults. Patients with PM or DM develop symmetric proximal muscle weakness progressive over weeks to months.

Pharyngeal or diaphragmatic weakness is common. EMG shows low-amplitude, small myopathic units with evidence of fibrillation potentials and/or positive sharp waves.

CK is usually markedly elevated.

Magnetic resonance imaging of affected muscles can show increased T2 signal secondary to edema, inflammation, or fibrotic replacement. 

Unique to DM are cutaneous manifestations that typically present at the same time as the weakness.

A purplish discoloration involving the eyelids, cheeks and nose (heliotrope rash), or an erythematous rash often seen on the knuckles (Gottron’s papules), are both pathognomonic for DM.

A rash on the neck and upper chest (V sign), shoulders (shawl sign), or extensor surfaces of elbows, knees, hips, and medial malleoli (Gottron’s sign) can also be seen. The rash often worsens with exposure to sunlight.

Skin may become scaly and atrophic, and the nail beds may appear shiny and red. Subcutaneous calcification over pressure points is more common in juvenile-onset DM. 

Patients can develop symptomatic systemic involvement, including fever, weight loss, cardiac arrhythmias and conduction abnormalities, interstitial lung disease (10% to 20%), conjunctivitis/uveitis, calcinosis, and gastrointestinal (GI) abnormalities.

Myositis-specific autoantibodies, found in 60% to 80% of patients with autoimmune myopathies, can help diagnose as well as predict systemic involvement.

The most common is antisynthetase syndrome, most associated with the presence of anti-Jo-1 antibody.

These patients have a constellation of clinical symptoms including autoimmune myopathy, interstitial lung disease (ILD), nonerosive arthritis, fever, and “mechanic’s hands,” hyperkeratotic lesions on the palmar fingers.

Autoantibodies in Dermatomyositis

AntibodyPhenotype
Jo-1 (PL-7, PL-12, EJ, OJ)Antisynthetase syndrome
Mi-2Classic DM, more rash, less malignancy
TIF-1γ, TIF-1αCancer-associated DM
NXP-2Juvenile DM, more calcinosis
SAESevere skin findings, mild myositis
MDA5More severe ILD, mild myositis, Asians

DM = Dermatomyositis, ILD = Interstitial lung disease

Both PM and DM also have been associated with malignancies, in particular lung, GI, breast, and ovarian cancers. All patients with DM or PM should be screened for malignancy. 

Sources

Mammen AL: Autoimmune myopathies: autoantibodies, phenotypes and pathogenesis. Nat Rev Neurol 7, 343–354, 2011.

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