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M08.028.002 Muscles Inflammatory myopathies
Inflammatory myopathies are a group of autoimmune disorders characterized by chronic inflammation of skeletal muscle, leading to progressive muscle weakness. This section delves into three main types encountered in clinical practice: Polymyositis, Dermatomyositis, and Inclusion Body Myositis. Understanding their presentations, pathology, and management is essential for medical students.
Polymyositis
Description:
- Autoimmune disease primarily affecting adults.
- Presents with symmetrical weakness in proximal muscle groups (shoulders, hips, thighs).
Microscopic Findings:
- Endomysial lymphocytic inflammation (predominantly cytotoxic T8 lymphocytes).
- Skeletal muscle fiber degeneration and regeneration.
Treatment:
- Responds well to immunosuppressive therapy.
Table 1. Summary of Polymyositis Characteristics
| Feature | Description |
|---|---|
| Type | Autoimmune |
| Age of Onset | Adults |
| Muscle Weakness | Symmetrical, proximal |
| Microscopic Findings | Endomysial inflammation, fiber degeneration/regeneration |
| Treatment | Immunosuppressive therapy |
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Points to Remember:
- Polymyositis is an idiopathic autoimmune disease (cause unknown).
- Early diagnosis and treatment are crucial to prevent muscle weakness progression.
Dermatomyositis
Description:
- Connective tissue disorder involving both skeletal muscle and skin inflammation.
- Can affect both children and adults.
Clinical Features:
- Symmetrical, proximal muscle weakness.
- Characteristic skin rash involving the upper eyelids (heliotrope rash) and periorbital edema (facial puffiness).
Microscopic Findings:
- Perimysial and vascular lymphocytic inflammation.
- Perifascicular fiber atrophy (wasting of muscle fibers around a nerve fascicle).
- Skeletal muscle fiber degeneration and regeneration.
Clinical Correlate:
- Anti-tRNA synthetase antibodies, particularly anti-Jo-1, are highly specific markers for inflammatory myopathies.
Table 2. Summary of Dermatomyositis Characteristics
| Feature | Description |
|---|---|
| Type | Connective tissue disorder |
| Age of Onset | Children and adults |
| Muscle Weakness | Symmetrical, proximal |
| Skin Rash | Heliotrope rash, periorbital edema |
| Microscopic Findings | Perimysial/vascular inflammation, fiber atrophy, degeneration/regeneration |
| Marker | Anti-tRNA synthetase antibodies (e.g., anti-Jo-1) |
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Points to Remember:
- Adult patients with Dermatomyositis have an increased risk of developing cancer.
- Early diagnosis and treatment are essential to manage muscle weakness and prevent complications.
Note: Skeletal muscle fiber type is determined by the innervating nerve.
Inclusion Body Myositis
Description:
- Affects adults over 50 years old.
- Presents with slowly progressive, asymmetrical weakness in distal muscle groups (hands, forearms).
Microscopic Findings:
- Autophagic vacuoles (intracellular structures for degradation).
- Inclusion bodies within muscle fibers.
- Inflammation and muscle fiber necrosis (cell death).
Treatment:
- Refractory to immunosuppressive therapy.
Table 3. Summary of Inclusion Body Myositis Characteristics
| Feature | Description |
|---|---|
| Age of Onset | >50 years old |
| Muscle Weakness | Slowly progressive, asymmetrical, distal |
| Microscopic Findings | Autophagic vacuoles, inclusion bodies, inflammation, necrosis |
| Treatment | No effective treatment |
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Points to Remember:
- Inclusion Body Myositis is the most common inflammatory myopathy in older adults.
- There is currently no cure, but supportive therapy can help manage symptoms.
Bibliography:
- Kumar, Vinay, et al. Robbins Basic Pathology. Elsevier, 2018.
- Ferri, Fred F. Ferri’s Clinical Advisor 2023. Elsevier Health Sciences, 2022.
- [Insert additional relevant medical pathology resources]