6. INFLAMMATORY MYOPATHIES-1 Year 4 Internal Medicine Notes

6. INFLAMMATORY MYOPATHIES-1 Year 4 · Internal Medicine Collection: 4TH YEAR ALL NOTES / IMED / IMED 4.3 / NGUGI -- Slide 1 IDIOPATHIC INFLAMMATORY MYOPATHIES Michael Ombasa Rebecca Jeptanui Slide 2 Introduction Inflammatory myopathies are a group of rare autoimmune disorders that primarily affects the muscles, causing inflammation and muscle weakness. These conditions are characterized by the immune system mistakenly attacking healthy muscle tissue, leading to various symptoms and complications. Slide 3 History The recognition of Idiopathic inflammatory myopathies began in the late 19th and early 20th centuries. Dermatomyositis was first described by the dermatologist Unna in 1891. Polymyositis was initially recognized as a distinct entity in the 20th century. Slide 4 Classification The classification of Idiopathic inflammatory myopathies has evolved over time and it includes several subtypes.\nDermatomyositis. Polymyositis. Inclusion body myositis. Slide 5 Epidemiology Annual incidence 0.2-1:100,000\nPrevalence of 2-25:100,000\nEpidemiology remains unclear in Africa. Risk factors Genetics Environmental Infections Medications Malignancy\nGeography. Slide 7 POLYMYOSITIS Muscular and extra muscular involvement. Manifests in adults more commonly in women, over the age of 20 years (not usually seen in childhood) It can be associated with heart, lung and joint involvement as well as increased risk of cancer. Presentation Progressive neck flexor and symmetric proximal limb muscle weakness which develops over weeks to months. The large muscle groups e.g shoulder and hip muscles are affected. The distal muscles are spared. Dysphagia occurs in one-third of the patients.\nMyalgias and tenderness are the most common complaints. Slide 9 Pathogenesis The exact pathogenesis of polymyositis is not fully understood.\nCell mediated cytotoxic immune response. CD8+ cytotoxic T cells invade the muscle fibres that express MHC class 1 antigens which may lead to fibre necrosis via the perforin pathway. Factors triggering the cell mediated process are unclear. However viruses have been implicated and the include HIV, HTLV. These viruses may directly invade the muscle tissue, damaging the vascular endothelium and releasing cytokines, which then induce abnormal expression of MHC and render the muscle susceptible to destruction. Genetic variability in HLA genes is also thought to play an important role in polymyositis. This may partly be attributed to the influence of HLA molecules in T-cell receptor development, peripheral tolerance and immune response to environmental agents. Slide 10 Histology Muscle Biopsy Features\n- Fibre size variability cellular invasion of non-necrotic muscle fibres and expressing MHC- antigens Scattered necrotic and regenerating fibres. Slide 11 Clinical Features Weakness: Progressive muscle weakness is the hallmark symptom of polymyositis. It typically affects the proximal muscles, such as those around the shoulders, hips, and thighs. This weakness can make activities like climbing stairs, rising from a chair, or lifting objects difficult. Symmetrical Involvement: The muscle weakness in polymyositis usually affects both sides of the body symmetrically. This means that if a muscle group on one side is affected, the corresponding muscle group on the other side is also likely to be affected. Fatigue: Patients with polymyositis often experience fatigue, which can be severe. This fatigue may not always correlate with the degree of muscle weakness and can impact daily activities. Pain and Tenderness: Muscles affected by polymyositis can be painful and tender to the touch. This is more common during active phases of the disease Slide 12 Cont. 5.Difficulty Swallowing (Dysphagia): In some cases, polymyositis can affect the muscles involved in swallowing, leading to difficulty in swallowing. This can result in choking or aspiration. 6.Joint Pain: Joint pain and inflammation may occur in addition to muscle symptoms. Joints are not the primary target in polymyositis, but some patients may experience arthralgia (joint pain). 7.Skin Changes: Dermatological manifestations, such as a skin rash, may occur in some cases. Gottron's papules, which are raised, scaly areas over the knuckles, and a heliotrope rash (a purple rash on the upper eyelids) are characteristic skin findings. 8.Systemic Symptoms: Some individuals with polymyositis may experience systemic symptoms such as fever, weight loss, and general malaise. 9.Respiratory Involvement: In severe cases, there can be involvement of respiratory muscles, leading to breathing difficulties. This can be a serious complication and may require medical intervention. Slide 13 Polymyositis work up. Increased creatine kinase up to 50 times normal or higher. Myositis specific antibodies. Imaging- MRI and ultrasonography to document and analyze the extent of muscle involvement. Electromyography- Abnormal finding in 90% of patients with polymyositis. evidence of membrane irritability