| What are idiopathic inflammatory myopathies? | Rare heterogenous muscle disorders, chronic and progerssive symmetrical proximal muscle weakness, can result in impaired indurance and disability, may be isolated muscle disorder, can be associated with other CT disorders [sjogren, SSc, SLE, RA].
Subclassified into polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM) with some other new subtypes (necrotizing, chronic granulomatous sarcoidosis, orbital, focal)
We have serology of myositis specific and myositis associated antibodies (MSA and MAA). |
| How is epidemiology of myositis? | Adults and children, PM and DM are most common in females 2:1, rare diseases 2 in million, peak incidence in age 50-60, incidence of IBM is 1 in million adults and more common in males, rarely occurs before age 50 |
| What are the etiopathogenetic factors of myositis? | Genetic (autoimmune diseases, HLA II alleles defects)
Environmental (infections [coxsackie, flu, retro, trypanosoma], UV exposure and vitamin D [Anti MI2 Ab [uv] and anti-Jo 1 [vitD}], Drugs [statin, fibrate, nicotinic acid, cimetidine, chloroquine.
Statin induced is very rare, HMGCoA reductase inhibitors so we get HMGCR antibodies]) |
| How is the pathogenesis of myositis? | Adaptive immunity (T cells, B cells, autoantibodies and D c)
T cells (PM high proportion of CD8 T cells then CD4 T cells in endomysial infiltrates, DM more CD4 and macrophages in perivascular localisation in perimysium, CD28 null T cells can persist in muscles for a long time and resist immunosupressive therapy, Th17)
B cells are less commonly found in infiltrates and more often perivascular localization in DM infiltrate, autoantibodies produced, pathogenic role increase with pathology, make antibody dependent cellular cytotoxicity and complement fixation |
| What are the muscle clinical features of PM/DM? | Muscle weakness with impaired muscle indurance and excessive muscle fatigue, weakness most seen in proximal muscle groups with subacute/insidious onset and symmetrical distribution.
In untreated cases muscle weakness progresses slowly lead to severe cases (wheelchair dependence, dysphagia, risk of aspiration pneumonia, airway needs protection, voice alteration, breathing difficulties) |
| What are the skin manifestations in DM? | Months-years before muscle involvement, aggravated by UV, complain of itching/pain, non-specific histo, so unhelpful biopsy.
Gottron's Papule (plaque, 1mm thick, violaceous, dusky red papules over dorsal side of metacarpal/interphalangeal joints)
Heliotropic rash (periorbital erythema of eyelid)
Shawl sign (erythema over neck, shoulders and chest)
Hostler sign (erythema over hips)
periungual nailfold telengectasis/cuticular hemorrhage infarct/dystrophy)
Mechanic hand (hyperkeratosis, scaling and fissuring, radial side of index finger, associated with Anti-Jo 1 antibodies in Antisynthetase syndrome (ASS)
Severe generalised erythema, panniculitis, livedo reticularis, non-scarring alopecia/vestibulobollus lesions, cutaneous calcinosis in juvenile DM>adult pressure or friction sites dorsal of elbow, visible in skin or muscle Xray/MRI. |
| What are the lung clinical manifestations of myositis? | Involved 5-65%, dyspnea and cough, ILD caused by inflammation of alveoli followed by pulmonary fibrosis in untreated cases leading to restrictive lung disease, weakness of respiratory muscles aggrevate dyspnea, detected by HRCT and PFT and CO diffusion capacity |
| What are the muscloskeletal clinical manifestations of myositis? | arthralgia and arthritis are common in IIM, especially ASS pt anti jo 1, arthritis affects small joints of hands and feet and are non-erosive |
| How is malignancy seen in myositis? | High risk 30%, more in men and old age, at time of DM diagnosis or during the first year of dx, cancers associated are lung, ovary, breast, colon and rare hematologic. Paraneoplastic phenomenon is of malignancy, screen of cancer for DM patients (at dx and yearly for first years, or following a relapse in those refractory to conventional immunosuprressive tx) |
| What is ASS? | Anti synthetase syndrome, anti-t-RNA synthetase antibodies (anti-Jo-1) directed against histidyl-t-RNA synthetase, myositis, ILD, Raynaud's phenomenon, non-erosive symmetrical polyarthritis in small joints, scaly skin changes in hands called mechanic's hand. |
| How is dx of myositis done? | HX, PE, Labs (CPK, myoglobin, aldolase), Biopsy, Electromyography (motor unit potentials), Muscle MRI (gold std for study detailed view of muscle involvement, symmetrical edema T2 images and fatty atrophy T1 images)
Biopsy (important to confirm inflammatory and muscle fiber changes, distinguish PM from IBM, exclude other myopathies, PM>DM, negative biopsy doesnot exclude myositis may be focal,
Mononuclear infiltrates and muscle fiber necrosis common with all myositis.
PM (MHC I cells invade), DM (perifascicular atrophy and microangiopathy), Immune mediated necrotizing myopathy (random necrosis w/out mononuclear infiltrate), Sporadic inclusion body myositis (endomysial inflammation, rimmed vacuoles and muscle fiber degeneration) |
| How is the prognosis of myositis? | • Before corticosteroids era patients with myositis had a high risk of developing deep muscle weakness and consequent severe disability
• premature death, mainly due to pulmonary complications, such as aspiration pneumonia or interstitial lung disease
• Treatment with corticosteroids immunosuppressants and, more recently, new biologic drugs has substantially improved IIM patients survival, quality of life and disability
• mortality among IIMs patients remains two- to threefold higher than the general population; most common causes of death are cancer, lung and cardiac complications, and infections.
• 20 to 40 disease remission and very few recover full normal muscle function,
• 60-80% of treated patients will experience a polycyclic or chronic continuous course of the disease
• Poor prognostic factors in IIMs patients are
• older age,
• male gender,
• non-Caucasian ethnicity,
• longer symptom duration,
• ILD, cardiac involvement, dysphagia, cancer,
• specific serologic pattern (including coexistence of anti-Ro52 and anti-Jo1 antibodies, presence of anti-signal recognition particle antibody, anti-155/140, and
anti-CADM-140 antibodies |
