What are the symptoms and treatment of polymyositis?

Symptoms and Treatment of Polymyositis

Key Symptoms of Polymyositis

Polymyositis is characterized by symmetric proximal muscle weakness, elevated muscle enzymes (CK, LDH, AST), and inflammatory infiltrates on muscle biopsy. 1

The clinical presentation typically includes:

• Proximal muscle weakness - Most commonly affecting:

  • Neck flexors and extensors
  • Shoulder girdle muscles (trapezius, deltoid)
  • Hip girdle muscles
  • Progressive difficulty with activities like climbing stairs, rising from chairs, or lifting arms overhead 2, 3

• Pattern of weakness development:

  • May develop suddenly or insidiously over weeks to months 3
  • Predominantly affects proximal muscles
  • Can sometimes present with isolated upper limb and neck weakness (cervicobrachial variant) 2

• Associated symptoms:

  • Muscle pain in 57% of patients 2
  • Dysphagia and dysphonia due to involvement of striated muscles of upper esophagus 3
  • Respiratory symptoms from chest wall muscle involvement or interstitial lung disease 4
  • Cardiac involvement leading to arrhythmias or heart failure 3

• Laboratory findings:

  • Elevated muscle enzymes (median CK 1275 IU/L) 2
  • Positive autoimmune antibodies in some patients (ANA, RA, anti-Ro, anti-Jo-1) 2, 4
  • EMG showing inflammatory myopathy with fibrillation potentials 5

Treatment of Polymyositis

Initial Treatment

The recommended initial treatment for adult patients with biopsy-confirmed polymyositis is high-dose corticosteroids (prednisone 1 mg/kg/day) concurrent with a steroid-sparing agent such as methotrexate, azathioprine, or mycophenolate mofetil. 1

Treatment protocol:

1. Start with prednisone 1 mg/kg/day (up to 60 mg/day)
2. Begin tapering after 2-4 weeks depending on clinical response
3. Simultaneously initiate steroid-sparing agent:
   • Methotrexate (first-line)
   • Azathioprine (alternative)
   • Mycophenolate mofetil (alternative)

Treatment for Severe Disease

For patients with severe disease, more aggressive therapy may be warranted:

• IV methylprednisolone (1-2 mg/kg)
• Intravenous immunoglobulin (IVIG)
• Rituximab
• Consider intensive combined therapy with high-dose glucocorticoids, tacrolimus, and IVIG 1

Treatment Monitoring

Effective monitoring includes:

• Regular assessment of muscle strength
• Serial creatine kinase (CK) measurements (target low-normal range)
• Functional status improvement
• Ability to taper corticosteroids 1

Treatment Duration and Prognosis

• Treatment period should be long (average 27 months) 6
• Tapering should be gradual and slow
• Response to treatment typically begins around 7.4 weeks (range 1-12 weeks) 2
• 5-year survival rate for treated patients is approximately 95% 3
• Up to one-third of patients may be left with some degree of residual muscle weakness 3

Complications and Special Considerations

Respiratory Complications

• Interstitial lung disease (ILD) occurs in approximately 36% of patients 2
• Respiratory involvement is a major cause of morbidity and mortality 4
• Weakness of respiratory muscles can lead to hypercapnic respiratory failure 4

Cardiac Complications

• Progressive atrioventricular or intraventricular conduction defects
• Tachyarrhythmias
• Congestive heart failure 1, 3

Treatment Response Factors

Factors associated with better treatment response:

• Younger age
• Absence of associated malignancy or cardiac disease
• Treatment initiation within 24 months of symptom onset
• Higher initial steroid doses 6

Common Pitfalls in Diagnosis

• Polymyositis is often misdiagnosed initially as:

  • Motor neuron disease
  • Cervical radiculopathy
  • Brachial neuritis
  • Chronic inflammatory demyelinating polyradiculoneuropathy
  • Myasthenia gravis
  • Facioscapulohumeral muscular dystrophy 2

• The cervicobrachial variant with predominant upper limb and neck weakness is particularly prone to misdiagnosis, leading to treatment delays 2