Introduction
Polymyositis and Dermatomyositis stand as enigmatic entities within the spectrum of autoimmune diseases, characterized by their unique pathophysiology and clinical manifestations. In this extensive presentation, we embark on a journey to dissect the intricacies of these conditions, unraveling their underlying mechanisms, exploring diagnostic modalities, delineating treatment approaches, and delving into the lived experiences of individuals affected by these disorders.
Understanding Polymyositis and Dermatomyositis
Polymyositis and Dermatomyositis represent autoimmune disorders primarily affecting skeletal muscles and skin, characterized by inflammation and tissue damage. While both conditions share certain similarities, they also exhibit distinct features.
Etiology and Pathogenesis
The exact etiology of Polymyositis and Dermatomyositis remains elusive, but a combination of genetic predisposition, environmental triggers, and immune dysregulation is thought to play a role. In Polymyositis, the immune system targets the muscle fibers, leading to inflammation and muscle weakness. Dermatomyositis, on the other hand, involves not only muscle inflammation but also skin involvement, presenting with characteristic skin rashes.
Clinical Manifestations
The clinical presentation of Polymyositis and Dermatomyositis varies widely among individuals. Common symptoms include muscle weakness, fatigue, skin rashes, difficulty swallowing, and joint pain. Dermatomyositis is often associated with characteristic skin findings such as the classic heliotrope rash and Gottron's papules.
Diagnostic Evaluation
Diagnosing Polymyositis and Dermatomyositis can be challenging and often requires a combination of clinical evaluation, laboratory tests, and imaging studies. Serum muscle enzymes such as creatine kinase (CK) and aldolase may be elevated in both conditions. Electromyography (EMG) and muscle biopsy are valuable tools to confirm the diagnosis and assess the extent of muscle involvement.
Treatment Strategies
The management of Polymyositis and Dermatomyositis aims to control inflammation, alleviate symptoms, and prevent complications. Corticosteroids, such as prednisone, are the mainstay of treatment, often combined with immunosuppressive agents such as methotrexate or azathioprine for long-term management. Intravenous immunoglobulin (IVIG) and biologic agents may be considered in refractory cases.
Prognosis and Complications
The prognosis of Polymyositis and Dermatomyositis varies depending on factors such as disease severity, response to treatment, and the presence of complications. Early diagnosis and aggressive management can improve outcomes and reduce the risk of long-term disability. Complications may include muscle atrophy, joint contractures, interstitial lung disease, and malignancy.
Research Advances
Ongoing research efforts continue to expand our understanding of the pathogenesis of Polymyositis and Dermatomyositis and identify novel
2. 2
Polymyositis
• Characterized by an inflammatory process affecting
skeletal muscle
Dermatomyositis
• Describes the same but with skin involvement
Both are subtypes of idiopathic inflammatory myopathies
DEFINITIONS
3. 3
Pathophysiology
Immunogenetic and cellular
predisposition
Genetic contribution
Increase in autoantibodies
(anti-Jo-1/Anti-Mi-2)
Malignancy
Tumor cells increase the systemic
inflammatory response
Environmental triggers
Infectious agents (e.g picornavirus)
or drugs ( statins)
Autoantibodies bind to DNA or RNA in
muscles
Chemokines and cytokines in the
endothelial vasculature of muscles
Perivascular inflammation Capillary necrosis
Gottron Papules
Heliotrope Rash
Dermatomyositis only
Hypoperfusion to the muscles, muscle ischemia, muscle tissue damage
Dermatomyositis: humoral
immune mechanism(CD4)
Polymyositis: cell-mediated
process (CD8)
4. 4
Clinical Features
• Age of onset : 40-60 years
• Gradual, over a few weeks
Features common in both myositis:
• Symmetrical proximal muscle weakness
• Usually affecting the lower limbs > upper
limbs
• Patients complain of:
• Difficulty rising from the chair
• Climbing stairs and lifting
• Difficulty combing hair
• Sometimes with muscle pain
5. 5
• Systemic features like fever, weight loss and
fatigue is common
• Respiratory or pharyngeal muscle involvement
can lead to ventilatory failure or aspiration
• Interstitial lung diseases (30%)
Polymyositis is usually widespread but focal
disease can also occur (orbital myositis)
There is about 3 –fold increased risk of
malignancy in patients with dermatomyositis and
polymyositis
10. 10
Laboratory:
• LDH, aldolase, AST,ALT raised
• ANA positive in 50% patients
• Anti-synthetase antibodies (anti-jo-1 antibodies)
• Anti signal recognition particle– cardiac manifestations
• Anti-Mi-2 antibodies– better prognosis
• Creatinine kinase
• Normal CK does not exclude (juvenile myositis)
Investigations
11. 11
Muscle Biopsy
• Fiber necrosis, regeneration
and inflammatory infiltrates
• Dermatomyositis: perimysium
• Polymyositis: endomysium
Occasionally, biopsy may be normal, if
myositis is patchy, in such cases do
MRI to identify areas
12. 12
• EMG
• To exclude neuropathy
• To confirm myopathy
Screening of underlying
malignancy:
• Chest/abdomen/pelvis
CT
• GIT imaging
• mammography
14. 14
Management
• Oral steroids (prednisolone 40-60 mg daily)
• In respiratory or pharyngeal weakness, IV
methylprednisolone (1g/day for 3 days)
• If good response to steroids, then reduce dose
of 25% per month up to 5-7.5 mg
• Additional therapy:
• Azathioprine, methotrexate
• IV immunoglobulins are effective in refractory
cases
• If the patient relapses--- additional therapy,
• If relapses or fails to respond to therapy– type
2 fiber atrophy (steroid-induced myopathy)
