Inflammatory Myopathies (IIM) Clinical Features

• Polymyositis and dermatomyositis (PM/DM) are inflammatory muscle disorders that require interprofessional team management.

• Corticosteroids are the initial therapy for PM/DM, but no guideline exists for dosing and tapering, so treatment should be under an experienced physician.

• Steroids have side effects, including osteoporosis, steroid-induced myopathy, hypertension, hyperglycemia, and weight gain, which need to be monitored and managed.

• Steroid-sparing agents, methotrexate and azathioprine, are used for patients with adverse effects to steroids or inadequate responses.

• Rituximab, an anti-CD 20 monoclonal antibody, is effective in treating myositis and myositis-related interstitial lung disease and is preferred over cyclophosphamide due to better tolerance.

• Tailored physical exercise programs and rehabilitation under a physiatrist or physical therapist improve muscle strength and decrease disability, even in patients with acute inflammatory myopathy.

• Dermatomyositis is characterized by a distinctive rash.

• Differential diagnosis includes other idiopathic inflammatory myopathies, drug-induced myopathies, motor neuron diseases, myasthenia gravis, Lambert-Eaton syndrome, hypothyroidism, muscular dystrophies, myotonic dystrophy, Amyotrophic lateral sclerosis, amyloid myopathy, and sarcoid myopathy.

• The outlook for patients with PM/DM is guarded.

• Figures and references in the article depict the appearance of a dermatomyositis rash and provide further reading on the topic.

• MHC Class I antigen expression is more frequent than MHC Class II in muscle, but the mechanism for induction is unknown.

• IIM (Autoimmune Myopathies) characterized by symmetric proximal muscle weakness and various skin findings.

• Major skin findings in dermatomyositis: Heliotrope rash (violaceous rash on eyelids), Gottron papules (erythematous rash on hands), Gottron sign (erythematous patches on elbows, knees, and ankles), Shawl sign (erythematous rash on chest and upper back), mechanic's hands (dilated capillaries, thickened cuticles, and cracked palmar fingertips), and Holster sign (poikiloderma on lateral thighs).

• Dermatomyositis includes hypomyopathic or amyopathic forms and has extramuscular manifestations like arthritis, Raynaud phenomenon, dysphagia, and interstitial lung disease.

• Evaluation of IIM: creatine phosphokinase (CPK) level measurement, serial muscle enzyme measurements, inflammatory markers (ESR, CRP), autoantibodies, muscle imaging, electrophysiologic examination, and muscle biopsy.

• Autoantibodies: Myositis-specific antibodies (MSA) like antisynthetases (anti-Jo-1, anti-Mi-2, anti-MDA5, anti-TIF, anti-SAE, anti-NXP) and dermatomyositis-associated antibodies (anti-PM SCL, anti-Ro, anti-La, anti-Ku, and anti-U1 RNP).

• Muscle evaluation: EMG (low amplitude, short duration, and polyphasic potential, increased membrane irritability, spontaneous fibrillation, and early recruitment) and MRI (STIR sequence for inflammation, T1 sequence for atrophy and scarring).

• Chest X-ray to detect lung involvement and age-appropriate cancer screening (colonoscopy, low dose CT chest, Pap smear, mammogram, and PET/CT scans for anti-NXP2 or anti-TIF positive patients).

• Treatment: Corticosteroids and other immunosuppressants.

• Malignancy is more prevalent in IIM, particularly dermatomyositis.

• IMM has distinct phenotypes and specific autoantibodies associated with each phenotype.

• Hypomyopathic or amyopathic dermatomyositis patients have little or no muscle involvement.

• Extramuscular manifestations include arthritis, Raynaud phenomenon, dysphagia, and interstitial lung disease.

• Muscle enzyme measurement, inflammatory markers, autoantibodies, muscle imaging, electrophysiologic examination, and muscle biopsy are used for diagnosis and evaluation.

• Corticosteroids are the initial therapy for managing both PM and DM.

Test your knowledge about the clinical features of Inflammatory Myopathies (IIM), including symmetric proximal muscle weakness and associated symptoms.