From the Guidelines
Polymyositis presents with progressive, symmetric muscle weakness that typically begins in the proximal muscles (shoulders, upper arms, hips, and thighs) and develops over weeks to months, as reported in the most recent study 1. Patients often report difficulty with everyday activities like climbing stairs, rising from a seated position, lifting objects, or combing their hair. Muscle pain (myalgia) and tenderness may occur but are less common than weakness. Fatigue is frequently reported. Some patients experience dysphagia (difficulty swallowing) or dysphonia (voice changes) if throat and neck muscles are affected. Respiratory muscle involvement can lead to breathing difficulties in severe cases. Associated symptoms may include fever, weight loss, Raynaud's phenomenon, and arthralgia. Skin manifestations are notably absent in polymyositis (unlike dermatomyositis). Laboratory findings typically show elevated muscle enzymes (creatine kinase, aldolase), and patients may have positive autoantibodies. The condition results from an autoimmune process where T-cells attack muscle fibers, causing inflammation and damage. Early recognition is crucial as prompt treatment with corticosteroids (typically prednisone 1mg/kg/day) and immunosuppressants (such as methotrexate, azathioprine, or mycophenolate mofetil) can prevent irreversible muscle damage and improve outcomes, as recommended in the latest guidelines 1.
Key points to consider in the management of polymyositis include:
- Grading of myositis severity, with mild (G1) to severe (G3-4) symptoms guiding treatment decisions 1
- Use of corticosteroids, such as prednisone, as the first-line treatment for polymyositis, with dosages ranging from 0.5-1 mg/kg/day for mild symptoms to 1-2 mg/kg/day for severe symptoms 1
- Consideration of immunosuppressants, such as methotrexate, azathioprine, or mycophenolate mofetil, for maintenance therapy or in cases where symptoms do not resolve entirely after 4 weeks of corticosteroid treatment 1
- Referral to a rheumatologist or neurologist for patients with moderate to severe symptoms, and consideration of hospitalization for patients with severe weakness, respiratory compromise, or rhabdomyolysis 1.
Overall, prompt recognition and treatment of polymyositis are essential to prevent irreversible muscle damage and improve patient outcomes, as emphasized in the latest study 1.
From the Research
Signs and Symptoms of Polymyositis
- Muscle pain and weakness are common symptoms of polymyositis, with 55% of patients experiencing these symptoms along with characteristic EMG and/or muscle biopsy findings 2
- Proximal muscle weakness is a predominant symptom, often presenting subacutely with mild diffuse muscular pain 3
- Some patients may experience atypical presentations, such as early respiratory difficulty, motor neuron disease, or isolated dysphagia, which can lead to delays in diagnosis and treatment 3, 4
- Respiratory symptoms, including diaphragmatic weakness and respiratory failure, can occur in some cases of polymyositis, even with relatively well-preserved power in limb muscles 4, 5
- Elevated serum creatine kinase levels and electrophysiologic abnormalities are also common in polymyositis, with 64% of cases showing raised serum creatine kinase activity 2
- Muscle biopsy is a key diagnostic tool, with 65% of biopsies showing changes with inflammatory infiltration virtually diagnostic of polymyositis 2
Clinical Characteristics
- The female to male ratio in polymyositis is approximately 1.4:1, with the largest number of cases occurring in the sixth decade of life 2
- The sedimentation rate is raised in 55% of cases, and electromyography is characteristic of polymyositis in 45% of cases 2
- Some patients may have a normal muscle biopsy, with 17% of cases showing no abnormalities 2