Specialty Neurology Neurology Chapter 5 5 Specific Conditions Polymyositis (PM); Dermatomyositis (DM); Inclusion body myositis (IBM) Polymyositis (PM) Dermatomyositis (DM) Necrotising autoimmune myopathy (NAM) of Evidence Evidence of probable benefit (Category 2a). PM and DM – Evidence of probable benefit (Category 2a). NAM – Small case studies only, insufficient data (Category 4a) Level of evidence was confirmed for all specific conditions. Description and Diagnostic Criteria The inflammatory myopathies are a group of three discrete disorders of skeletal muscle: DM, PM and IBM. These disorders are acquired and have in common the occurrence of significant muscle weakness and the presence of an inflammatory response within the muscle. The diagnosis of DM, PM or IBM is usually made by neurologists or rheumatologists, and relies on Dermatomyositis and polymyositis are idiopathic inflammatory myopathies. Necrotizing autoimmune myopathy typically has necrotic myofibres with less inflammatory infiltrate and the absence of direct myocyte invasion by lymphocytes. These disorders are acquired and have in common the occurrence of significant muscle weakness and the presence of an inflammatory response within the muscle. The weakness usually develops subacutely but may be chronic and present over many months. Proximal muscles are predominantly affected in a symmetric fashion. Diagnostic criteria have been revised and updated including NAM. (A)
the combination of careful clinical evaluation, an elevated creatine kinase level, electromyography and muscle biopsy. he diagnosis of DM, PM and NAM relies on the combination of careful clinical evaluation, an elevated creatine kinase level, electromyography and muscle biopsy. NAM is often associated with a history of statin exposure, and the presence of autoantibodies against HMG coenzyme reductase, or other muscle antigens. Justification for Evidence Category PM: The Biotext (2004) review included one prospective case-series study of 35 adults with chronic refractory polymyositis. IVIg may be of benefit in these patients, improve mean muscle power and allow reduction in dose of corticosteroid. Further research is needed. DM: The Biotext (2004) review included one double-blind, placebo-controlled considered of low quality of 15 patients with biopsy-confirmed, treatment-resistant dermatomyositis. IVIg treatment combined with prednisone led to significant PM: The Biotext (2004) review identified one prospective case-series study of 35 adults with chronic refractory polymyositis. This study reported clinical improvement in 71% of patients with significant improvement in muscle power, muscle disability scores and CK levels (p < 0.01). Steroid dose could be reduced after IVIg (p < 0.05). Further research is needed. DM: The Biotext (2004) review identified one double-blind, placebo-controlled trial considered of low quality of 15 patients with biopsy-confirmed, treatment-resistant dermatomyositis. IVIg treatment combined with prednisone led to significant improvement in muscle strength and neuromuscular symptoms of patients in the intervention group (n = Justification for evidence revised and updated (A)
Indications Patients with PM or DM with significant muscle weakness unresponsive to corticosteroids and other immunosuppressive agents. Patients with IBM who have dysphagia affecting function. Patients with rapidly progressive IBM. with biopsy-proven PM or DM or NAM who have significant muscle weakness or dysphagia unresponsive to corticosteroids and other immunosuppressant agents. Indication is qualified to note the requirement for muscle biopsy. SWG reported that there is a small subset of patients in whom dysphagia worsens following the introduction of steroids, despite improvement in limb weakness, who may require 3-6 months of IVIg for resolution of the dysphagia. Qualifying Criteria Diagnosis made by a neurologist, rheumatologist or immunologist of: Patients with PM or DM who have significant muscle weakness or dysphagia and have not responded to corticosteroids and immunosuppressive agents; OR Patients with IBM who have dysphagia with biopsy-proven PM or DM or NAM who have significant muscle weakness or dysphagia unresponsive to corticosteroids and other immunosuppressant agents. [Group 1] Patients with biopsy-proven PM, DM or NAM AND [Group 2] The MRC Sum (12) Score will be used to assess muscle weakness and determine response at review. Video-fluoroscopy will be used to demonstrate the involvement of pharyngeal muscles. SWG considered the application of disability scales at length - however, there is no commonly used or validated disability scale that can be practically used in the clinic setting for PM/DM– all those identified in the literature are research based and too time consuming for use in outpatient clinics. trial
Stabilisation of disease as defined by stable functional scores (ADLs) or quantitative muscle scores or MRC muscle assessment previous evidence of deterioration in one of these scores. food textures and/or reduced episodes of aspiration On review of a continuing authorisation period Patient demonstrating stabilisation or improvement in muscle weakness as measured by MRC Sum (12) Score (greater than or equal to the previous review score). OR Patient demonstrating stabilisation or improvement in dysphagia as assessed by speech therapy, improved tolerance of food texture and/or reduced episodes of aspiration AND A trial off Ig therapy is planned or a valid reason is provided as to what a trial is not being planned or is contraindicated at this time. review score must be greater than the qualifying score.