What is Myelitis?
Myelitis is inflammation of the spinal cord that can result from infectious, autoimmune, or post-infectious causes, leading to motor, sensory, and autonomic dysfunction with potentially devastating neurological consequences. 1, 2
Definition and Pathophysiology
Myelitis represents an inflammatory disease of the spinal cord, regardless of the underlying etiology or pathologic-anatomic alterations 3. The condition encompasses:
- Direct infectious invasion of the spinal cord by viral, bacterial, parasitic, or fungal pathogens
- Immune-mediated inflammation including autoimmune disorders (multiple sclerosis, neuromyelitis optica spectrum disorders, MOG-antibody associated disease)
- Post-infectious or post-vaccinal immunological processes 1, 3
The pathogenic mechanisms involve both direct replication of pathogens within the central nervous system and immune system responses that contribute to neurological damage 4.
Clinical Presentation
Symptoms typically develop over hours to days, then worsen over days to weeks 2:
- Motor dysfunction: Weakness ranging from mild paresis to complete tetraplegia with respiratory insufficiency
- Sensory alterations: Numbness, paresthesias, pain
- Autonomic dysfunction: Bowel and bladder problems, temperature dysregulation, hypertension episodes
- Prodromal illness: Many patients report preceding respiratory or febrile illness 5
Up to two-thirds of patients experience moderate to severe residual disability, making rapid diagnosis and treatment critical 2.
Diagnostic Patterns
Key MRI Lesion Patterns 6
The differentiation of medullary lesion patterns is crucial for diagnosis:
- Longitudinally extensive transverse myelitis (LETM): Contiguous lesions extending ≥3 vertebral segments, characteristic of NMOSD and MOGAD 7
- Short ovoid and peripheral lesions: Typical of multiple sclerosis
- Polio-like appearance: Anterior horn involvement, seen in acute flaccid myelitis 5
- Granulomatous nodular enhancement: Suggests infectious or sarcoid etiology
Clinical Distinction
Acute complete transverse myelitis versus acute partial transverse myelitis helps categorize entities, with the latter frequently being the onset of multiple sclerosis 6.
Diagnostic Workup
Essential investigations include 2, 3:
- Spinal MRI: Most critical test to identify lesion extent, edema, and rule out compressive etiologies (which require emergent surgical intervention)
- Cerebrospinal fluid analysis: Pleocytosis, protein levels, oligoclonal bands, infectious studies
- Serological testing: AQP4-IgG, MOG-IgG antibodies using cell-based assays 7
- Blood cultures and autoimmune panels
- Brain MRI: Mandatory in suspected demyelinating, systemic autoimmune, infectious, paraneoplastic, and metabolic diseases 6
Common Pitfalls
- Compressive myelopathy and transverse myelitis are clinically indistinguishable - neuroimaging must be performed urgently to avoid missing surgical emergencies 2
- NMOSD may start as short transverse myelitis and should not be mistaken for MS 6
- MOG-IgG testing requires cell-based assays with full-length human MOG; peptide-based ELISA and Western blot are obsolete 7
Prognosis
The clinical course varies from temporary sensory deficits to persistent tetraplegia 3. Rapid initiation of appropriate treatment based on specific etiology portends more favorable outcomes 2.