What are the characteristic presentations of adult onset overlap myositis?
- • Antisynthetase antibody (ASA) syndrome
- a. Proximal muscle weakness is typically the first manifestation. CPK usually 5 to 10 times upper limit of normal.
- b. Mechanic’s hand is common: characterized by cracking and fissuring of the skin of the finger pads, especially the radial side of the index finger.
- c. Some patients may have DM-like rash with heliotrope or Gottron’s papules and no mechanic’s hands.
- d. ILD, arthritis, Raynaud’s phenomenon, and fever can also occur. Rare association with cancer in older patients. ILD can be first and most severe manifestation in some clinical subsets of ASA syndrome.
- e. MSAs identify specific clinical subsets. Patients with both an MSA and anti-SSA/Ro (52kD) antibodies (30%) have worse disease.
- f. Muscle pathology: defined as immune myopathy with perimysial pathology with or without perifasicular atrophy. Looks more like DM but no complement deposition. A few patients may have a biopsy that looks more like PM (endomysial inflammation) or IMNM. HLA-DRβ1∗0301 is more common in these patients.
- g. Prognosis: 5YS 80%. Up to 33% of patients with ILD will lose lung function in spite of treatment.
- • Myositis associated with another connective tissue disease
- a. Most common overlap is myositis associated with systemic sclerosis. These patients frequently have MAA (anti-PM-Scl, anti-U1-ribonucleoprotein (RNP), anti-Ku, anti-U3RNP [fibrillarin]).
- b. Other connective tissue diseases associated with myositis include mixed connective tissue disease and SLE (frequently with anti-U1-RNP) and Sjögren’s syndrome. The MAA, anti-SSA/Ro (52kD), is also frequently seen.
- c. Some patients with a defined connective tissue disease and myositis can have MSA antibodies associated with an ASA syndrome. Suspect in connective tissue disease patients who develop myositis and/or ILD.
