Major diagnostic criteria for Polymyositis and dermatomyositis

Major diagnostic criteria for Polymyositis and dermatomyositis

What are their features

• Proximal motor weakness: weakness occurs earliest and insidiously over 3 to 6 months in most patients. It occurs most severely around the shoulder/pelvic girdles and neck flexors. Ocular and facial motor weakness is strikingly unusual and should make one consider another diagnosis. Pain is typically absent or minimal (25%) and if significant with more rapidly progressive weakness (<2 months) should suggest IMNM.

– Other striated muscle groups that can be involved include pharyngeal muscles causing dysphonia and upper esophageal muscles causing dysphagia (10%–30%). Nasal regurgitation of fluids can occur. Involvement of these muscles indicates more severe disease and associated with aspiration pneumonia.

• Elevated serum muscle enzymes: Creatine phosphokinase (CPK) is elevated in almost all patients at some time during the course of active disease. Other markers of muscle damage include elevated levels of aldolase, myoglobin, aspartate (AST) and alanine aminotransferase, and lactate dehydrogenase. Myoglobinuria can be seen in active disease.

– The combination of elevated CPK, aldolase, AST, and CPK muscle/brain (M/B) fraction >2% to 3% of total CPK is highly characteristic of an inflammatory myopathy. CPK M/B is released by regenerating skeletal muscle fibers (not the heart), which occurs in patients with an inflammatory myositis and not in other causes of myopathies. Notably, some PM/DM patients have an elevated aldolase but a normal CPK.

• MSAs and myositis-associated autoantibodies (MAA): Identify clinical subsets among the major categories of IIM. Patients with an IIM will only have one MSA since they are mutually exclusive. However, a patient with an MSA can also have a MAA particularly anti-Sjögren’s syndrome-related antigen A (SSA)/Ro (52kD).

• Abnormal neurodiagnostic studies: The electromyogram (EMG) in PM/DM has a good sensitivity (85%) but low specificity (33%). It shows a typical but not specific pattern consisting of: (1) increased insertional activity with spontaneous fibrillations, (2) myopathic low-amplitude and short-duration polyphasic motor unit action potentials, and (3) complex repetitive discharges. Nerve conduction velocity studies are normal in IIM, with the exception of IBM in which neuropathic disease can develop along with the myopathy.

• Muscle biopsy: Muscle biopsy should be performed in most cases to confirm the suspected diagnosis. The histologic pattern can be helpful both diagnostically and prognostically.

• Characteristic rash of DM: Skin biopsy shows interface dermatitis usually with mucin similar to systemic lupus erythematosus 

15585

Sign up to receive the trending updates and tons of Health Tips

Join SeekhealthZ and never miss the latest health information

15856