Guideline for Differentiating Acute Transverse Myelitis and Subacute Combined Degeneration

Clinical Presentation

Acute‑to‑subacute onset (hours‑to‑days, nadir within 2 weeks) with bilateral motor weakness, sensory loss below a level, and bowel/bladder dysfunction strongly suggests transverse myelitis. 1
A distinct sensory level is usually present in transverse myelitis; motor and sensory deficits are bilateral but may be asymmetric. 1, 2
Reflexes in transverse myelitis are variable—initially decreased or later hyperactive (upper‑motor‑neuron pattern). 2
Pain, often radicular or band‑like, is common in transverse myelitis. 1
Insidious, progressive onset over weeks‑to‑months with predominant sensory symptoms (paresthesia, numbness, loss of proprioception and vibration) points toward subacute combined degeneration (SCD). 3, 4
Early gait and sensory ataxia are characteristic of SCD due to dorsal‑column involvement. 3
Reflex pattern in SCD is mixed: loss of ankle jerks with preserved or increased knee jerks and possible extensor plantar responses. 3
Motor weakness in SCD typically develops later in the disease course. 3

Transverse myelitis lesions vary in length—short (< 3 vertebral segments) or longitudinally extensive (≥ 3 segments). 1
Lesions involve the central cord, affecting both gray and white matter. 2
Gadolinium enhancement is common in transverse myelitis, indicating active inflammation. 1, 2
Lesions can occur at any spinal level (cervical, thoracic, lumbar). 2
Cord swelling is frequently observed in the acute phase of transverse myelitis. 2
SCD shows symmetric T2‑hyperintensity confined to the dorsal and lateral columns only—pathognomonic for the disorder. 5, 4
No gadolinium enhancement is seen in SCD. 4
Cord swelling is absent in SCD. 4
The selective tract involvement without central gray‑matter signal distinguishes SCD from inflammatory myelitis. 5

In transverse myelitis, cerebrospinal fluid (CSF) pleocytosis and elevated protein occur in 50‑70 % of cases. 1, 2
Oligoclonal bands may be present, especially when a demyelinating etiology is suspected. 1
Autoimmune antibody testing (aquaporin‑4 IgG, MOG antibodies) is recommended in transverse myelitis work‑up. 1
Infectious work‑up (viral PCRs, bacterial cultures) should be performed when indicated. 1, 2
Low serum vitamin B12 (< 200 pg/mL) is the hallmark laboratory abnormality in SCD. 6, 4
Elevated methylmalonic acid (MMA) and homocysteine confirm functional B12 deficiency even with borderline B12 levels. 6
CSF is typically normal in SCD, helping to differentiate it from inflammatory myelitis. 4
Macrocytic anemia may accompany SCD, but neurological symptoms often precede hematologic changes. 3, 6

Time course: Acute onset (< 24 h‑to‑2 weeks) strongly favors transverse myelitis; subacute/chronic onset (weeks‑to‑months) suggests SCD. 7, 1, 3, 4
Neurological exam: Prominent sensory level with early motor weakness points to transverse myelitis; gait ataxia with loss of proprioception/vibration and preserved pain/temperature points to SCD. 1, 2, 3
MRI pattern: Central cord T2‑hyperintensity with gadolinium enhancement indicates transverse myelitis; symmetric dorsal/lateral column hyperintensity (“inverted V” or “dumbbell” sign) without enhancement indicates SCD. 1, 5
Laboratory confirmation: If MRI suggests transverse myelitis → lumbar puncture, autoimmune antibody panel, infectious studies. 1
If MRI suggests SCD → serum B12, MMA, homocysteine, and complete blood count. 6, 4

Administering folic acid before excluding or treating B12 deficiency can precipitate or worsen SCD. 6, 3
Normal or borderline B12 levels do not exclude SCD; up to 30 % of patients require MMA/homocysteine testing for confirmation. 6
Delay of high‑dose methylprednisolone in transverse myelitis worsens outcomes; treatment should begin within hours of diagnosis. 1, 2
A sharp sensory level raises suspicion for spinal cord pathology but does not differentiate the two conditions; MRI pattern is decisive. 8, 9

Transverse Myelitis – Immediate high‑dose intravenous methylprednisolone (1‑2 g daily for 3‑5 days). 1, 2
Consider intravenous immunoglobulin (2 g/kg over 5 days) if steroids are contraindicated or response is inadequate. 1
Plasma exchange is recommended for refractory cases. 2
Subacute Combined Degeneration – Prompt vitamin B12 replacement is essential. 6
With neurological involvement: hydroxocobalamin 1 mg intramuscularly on alternate days until clinical improvement, then 1 mg every 2 months lifelong. 6
Without neurological involvement: hydroxocobalamin 1 mg intramuscularly three times weekly for 2 weeks, then every 2‑3 months lifelong. 6
Urgent neurologist consultation is advised for any patient with neurological manifestations of SCD to prevent irreversible damage. 6