What are the causes and treatment options for dorsal spinal myositis?

Dorsal Spinal Myositis: Etiology and Treatment

Dorsal spinal myositis is primarily caused by autoimmune processes, infections, or medication-related immune reactions, and treatment should begin with NSAIDs followed by corticosteroids, with escalation to immunosuppressive agents for refractory cases based on disease severity.

Etiology of Dorsal Spinal Myositis

Dorsal spinal myositis represents inflammation of the muscles surrounding the thoracic spine. Several causes have been identified:

Autoimmune Etiologies

• Idiopathic inflammatory myopathies (polymyositis, dermatomyositis)
• Immune-mediated necrotizing myopathy
• Overlap syndromes with myositis including anti-synthetase syndrome 1
• Chronic non-bacterial osteitis (CNO) affecting paraspinal muscles 2

Medication-Induced

• Immune checkpoint inhibitor (ICPi) therapy - particularly PD-1/PD-L1 inhibitors 2
• Statin-induced myopathy affecting paraspinal muscles
• Local steroid injections (rare cases) 3

Infectious Causes

• Bacterial infections (pyogenic)
• Fungal infections (e.g., Aspergillus - rare but potentially fatal) 3
• Viral myositis

Other Causes

• Post-traumatic myositis ossificans (rare in spinal region) 4
• Paraneoplastic syndromes

Diagnostic Approach

Clinical Evaluation

• Assess pattern of weakness, pain distribution, and timing of symptom onset
• Check for associated symptoms (rash, arthritis, fever)
• Evaluate for systemic inflammatory signs

Laboratory Testing

• Muscle enzymes: Creatine kinase (CK), AST, ALT, LDH
• Inflammatory markers: ESR, CRP
• Myositis-specific autoantibodies panel
• If suspected infection: Blood cultures, specific pathogen testing

Imaging

• MRI with fat suppression techniques and STIR sequences (gold standard) 2
• [18F]FDG PET/CT - particularly useful for:
  • Early detection (within 14 days of symptom onset)
  • Patients with spinal hardware
  • Cases with inconclusive MRI 2

Confirmatory Testing

• Electromyography (EMG) - shows fibrillations and myopathic changes
• Muscle biopsy - definitive diagnosis in unclear cases

Treatment Approach

First-Line Treatment

• NSAIDs/COXIBs at maximum tolerated dosage 2
• Evaluate response after 2-4 weeks
• For mild symptoms, continue NSAIDs with regular monitoring

Second-Line Treatment (for insufficient response to NSAIDs)

• Corticosteroids:
  • For moderate disease: Prednisone 0.5-1 mg/kg/day 2
  • For severe disease: IV methylprednisolone 1-2 mg/kg or pulse therapy 2
• Consider early escalation to second-line therapy for:
  • Spinal lesions with risk of vertebral collapse
  • Significant accumulated skeletal damage 2

Third-Line Treatment (for refractory cases)

• Conventional synthetic DMARDs:

  • Methotrexate (preferred for inflammatory arthritis component)
  • Azathioprine
  • Mycophenolate mofetil 2

• Biologic agents:

  • TNF-α inhibitors (especially with associated fasciitis)
  • IL-6 receptor antagonists (preferred for polymyalgia-like symptoms) 2
  • Rituximab (for severe refractory myositis) 2

• Intravenous immunoglobulin (IVIG) for severe cases with:

  • Bulbar symptoms (dysphagia, dysarthria)
  • Respiratory involvement
  • Myocarditis 2

• Plasmapheresis for fulminant cases unresponsive to other therapies 2

Special Considerations

Monitoring and Follow-up

• Regular assessment of muscle enzymes and inflammatory markers
• Periodic imaging to evaluate treatment response
• Monitor for medication side effects, especially with long-term corticosteroid use

Complications to Watch For

• Vertebral fractures (common complication in inflammatory myositis) 5
• Myocardial involvement (potentially fatal)
• Respiratory muscle weakness
• Chronic fibrosis and muscle atrophy

Supportive Care

• Physical therapy to maintain muscle strength and prevent contractures
• Pain management
• Nutritional support if dysphagia present

Treatment Algorithm Based on Severity

1. Mild Disease (minimal weakness, normal function):

   • NSAIDs/COXIBs
   • Physical therapy
   • Monitor for progression

2. Moderate Disease (affecting daily activities):

   • Prednisone 0.5-1 mg/kg/day
   • Add methotrexate or azathioprine if steroid-dependent
   • Regular monitoring of muscle enzymes

3. Severe Disease (significant weakness, organ involvement):

   • IV methylprednisolone pulse therapy
   • Early addition of immunosuppressants
   • Consider IVIG or biologics
   • Monitor for cardiac and respiratory complications

4. Refractory Disease:

   • Combination therapy with multiple immunosuppressants
   • Biologics (rituximab, TNF-α inhibitors)
   • Referral to specialized centers 2

The prognosis depends on the underlying cause, with autoimmune myositis typically responding to immunosuppressive therapy while infectious causes require targeted antimicrobial treatment.