Table 1.

Differential diagnoses that may show longitudinal transverse myelitis on MRI

Differential diagnoses	MRI features
NMOSD* AQP4 antibody and MOG antibody–associated disease.	Central grey or holocord affected axially. Gadolinium enhancement—one-third ring enhancing. Spinal cord swelling. MOG antibody–associated disease involves conus more frequently than AQP4.18 (Note: 10%–15% NMOSD AQP4-Ab present with short lesions.)
Spinal cord infarction*	Most often anterior spinal artery territory infarctions—radiologically and clinically sparing the dorsal columns.† Pencil-like T2 hyperintensity over multiple segments, anterior horn cells most vulnerable to ischaemia (axially, ‘owl’s or snake eyes’). No contrast enhancement acutely but sometimes appears subacutely. Restricted diffusion in the first week but not invariably found.18
Malignancy	Primary intramedullary spinal cord tumour, most commonly an ependymoma in adults. Cord enlargement with variable contrast enhancement. Intramedullary metastasis, are enhancing lesions, sometimes with adjacent oedema resembling a LETM. Fludeoxyglucose uptake on positron emission tomography (FDG) PET-CT. Paraneoplastic*. Acute necrotic myelitis, described by Mancall and Rosales in 1964,19 clinically and radiologically resembles NMOSD. Paraneoplastic myelitis is more commonly progresses over weeks with symmetrical lateral tract LETM sometimes with enhancement. Imaging can be normal.18
Infective and postinfective transverse myelitis.	Can be short or LETM. Enterovirus and poliovirus—central grey matter anterior horn affinity. HIV—sometimes dorsal T2 hyperintensity resembles metabolic.
Connective tissue disorders, for example, rheumatoid arthritis, systemic lupus erythematosus and Sjögren’s syndrome	Identical appearance to NMOSD, AQP4-Ab positive in 75% of LETM cases in connective tissue disorders.
Sarcoid	Imaging features are variable but include subpial enhancement with central canal enhancement, ‘trident sign’ on axial images, often with leptomeningeal enhancement.18
Behcets	‘Bagel Sign’ pattern: a central lesion with hypointense core and hyperintense rim with or without contrast enhancement.18
Drugs and toxins, for example, Heroin*, intrathecal methotrexate, radiation and nitrous oxide	Heroin-related myelopathy can resemble NMOSD with hyperacute onset typically after taking heroin following a period of abstinence.30
MS	Lesions usually peripheral, less than half cross sectional area and less than two vertebral lengths rostrocaudally.
Dural arteriovenous fistula—direct communication between radiculomedullary artery and vein, frequently in a dural sleeve of a nerve root	Venous hypertension swells the cord with breakdown in the blood brain barrier breaks. An enhancing LETM often with conus involvement; sometimes with a pathognomonic, ‘missing piece sign’. Dorsal dilated perimedullary vessels enhance with contrast and flow voids on T2 images.31 32
Nutritional—B12, copper deficiency	T2 hyperintensity posterior and anterolateral columns. Rarely enhance. Copper deficiency similar with more central cord involvement.

*Denotes conditions that may present hyperacutely with clinical nadir reached in minutes to hours (<12 hours); remainder subacute with onset over days to 6 weeks or chronic.

†Other ischaemic cord syndromes include hemicord, posterior spinal artery and central cord syndromes as well as mixed patterns.

AQP4-Ab, aquaporin-4 antibodies; LETM, longitudinally extensive transverse myelitis; MOG, myelin oligodendrocyte glycoprotein; MS, multiple sclerosis; NMOSD, neuromyelitis optica spectrum disorder.