What is the diagnostic approach and treatment for a patient with suspected transverse myelitis versus Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)?

Distinguishing Transverse Myelitis from CIDP

Transverse myelitis and CIDP are fundamentally different conditions that can be reliably distinguished by the presence or absence of hyperreflexia: transverse myelitis presents with spastic paralysis and increased deep tendon reflexes due to upper motor neuron involvement, while CIDP presents with flaccid paralysis and areflexia due to peripheral nerve demyelination. 1, 2

Key Clinical Distinguishing Features

Reflex Examination (Most Critical)

• Transverse myelitis: Bilateral weakness with hyperreflexia (increased deep tendon reflexes) and spastic paralysis, indicating upper motor neuron pathology 1, 2
• CIDP: Symmetric weakness with areflexia or hyporeflexia (reduced/absent reflexes) and flaccid paralysis, indicating peripheral nerve involvement 3, 4, 5

Pattern of Weakness

• Transverse myelitis: Bilateral weakness developing rapidly over hours to days (typically maximal within 10 days), often with a clear sensory level corresponding to spinal cord lesion location 1, 6, 7
• CIDP: Progressive symmetric proximal and distal weakness evolving over at least 8 weeks, without a sensory level 3, 4, 5

Autonomic Dysfunction

• Transverse myelitis: Bladder dysfunction occurs in virtually all patients, with urinary retention being common; bowel dysfunction and severe erectile/sphincter disturbance are frequent 3, 1, 6
• CIDP: Autonomic dysfunction is typically absent or minimal 4, 5

Diagnostic Workup Algorithm

Initial Imaging (Mandatory First Step)

• MRI of spine with thin axial cuts through suspected lesion areas to detect T2 hyperintense lesions—this is essential for transverse myelitis diagnosis 3, 2
• MRI of brain with and without contrast to evaluate for demyelinating lesions and assess dissemination in space 3, 2
• If transverse myelitis is confirmed on imaging, CIDP is effectively excluded as these are anatomically distinct processes 1, 2

Electrodiagnostic Studies

• Nerve conduction studies are essential for CIDP diagnosis and will show demyelinating features (prolonged distal latencies, conduction velocity slowing, conduction block) 4, 5
• Normal nerve conduction studies effectively exclude CIDP but do not rule out transverse myelitis 4, 5

Cerebrospinal Fluid Analysis

• Transverse myelitis: Lumbar puncture shows elevated protein, lymphocytic pleocytosis (with possible neutrophils up to 10%), and typically negative oligoclonal bands (87-88% of MOG-associated cases) 3, 1, 6, 7
• CIDP: CSF shows elevated protein (often >45 mg/dL) with normal or minimally elevated cell count (albuminocytologic dissociation) 4, 5

Specific Antibody Testing for Transverse Myelitis Subtypes

• Aquaporin-4 IgG (serum): Positive in neuromyelitis optica spectrum disorder (NMOSD) 3, 2
• MOG-IgG (serum using cell-based assays): Positive in MOG-associated encephalomyelitis (MOGAD), particularly when there is conus medullaris involvement, steroid-dependent symptoms, or longitudinally extensive transverse myelitis (LETM ≥3 vertebral segments) 3, 1, 2

Additional Laboratory Studies

• For transverse myelitis: HIV, RPR (syphilis), vitamin B12, TSH, ANA, anti-Ro/La to exclude infectious, metabolic, and autoimmune mimics 3, 2
• For CIDP: Consider testing for IgG4 antibodies to nodal/paranodal proteins (contactin-1, neurofascin-155) in treatment-refractory cases 4

Treatment Approach Based on Diagnosis

Transverse Myelitis

• Grade 1 (mild): Permanently discontinue immune checkpoint inhibitors if drug-induced; methylprednisolone 2 mg/kg 3
• Grade 2-4 (moderate to severe): Methylprednisolone 1 g IV daily for 3-5 days, strongly consider IVIG 2 g/kg over 5 days 3
• Plasma exchange should be considered when steroids are insufficient, particularly in MOGAD 1
• Evaluate and manage urinary retention and constipation 3

CIDP

• First-line treatments (equally effective): Intravenous immunoglobulin (0.4 g/kg for 5 days), subcutaneous immunoglobulin, corticosteroids, or plasma exchange 3, 4
• Maintenance treatment is often required for years with careful adjustments to avoid under- or overtreatment 4
• Treatment-related fluctuations occur in 6-10% and may warrant repeating full treatment course 3
• Acute-onset CIDP should be suspected if patient has ≥3 treatment-related fluctuations or clinical deterioration ≥8 weeks after initial presentation that resembled Guillain-Barré syndrome 3

Critical Diagnostic Pitfalls

• Do not confuse hyperreflexia with areflexia—this single finding distinguishes upper motor neuron (transverse myelitis) from peripheral nerve (CIDP) pathology 1, 2
• LETM in young adults is rarely multiple sclerosis; MOGAD or NMOSD should be considered first 3, 2
• Poor performance or misinterpretation of nerve conduction studies frequently leads to CIDP misdiagnosis 4
• Symptomatic spinal cord lesions should not be excluded from diagnostic consideration in transverse myelitis, as their presence increases MS risk and diagnostic sensitivity 3
• In patients presenting with features resembling Guillain-Barré syndrome who develop ≥3 relapses or deterioration ≥8 weeks after onset, reconsider the diagnosis as acute-onset CIDP (~5% of initial GBS diagnoses) 3