Diagnosing transverse myelitis requires a combination of a neurological exam, spinal cord MRI, and laboratory tests to confirm inflammation in the spinal cord while ruling out other causes of the symptoms. There is no single test that confirms it. Instead, doctors piece together clinical findings, imaging, and spinal fluid results to reach a diagnosis, often within days of symptom onset.
How Symptoms Guide the Diagnosis
The diagnostic process starts with a neurological exam that looks for a pattern of dysfunction pointing to the spinal cord. Transverse myelitis causes motor, sensory, or autonomic problems (like bladder and bowel issues) that correspond to a specific level of the spine. During the exam, a doctor will test sensation across your body to find a “sensory level,” meaning a point on your trunk or limbs below which sensation changes. This level helps pinpoint where the inflammation is located.
The thoracic spine (mid-back) is affected in roughly 70% of cases, cervical (neck) in about 20%, and lumbar (lower back) in about 10%. Where the lesion sits determines what symptoms you’ll have. Thoracic lesions typically cause weakness and sensory changes in the legs. Upper cervical lesions can affect all four limbs and, if the inflammation reaches the C3 through C5 levels, it can impair the diaphragm and cause breathing difficulty. Back pain at the level of the inflammation is also common.
Symptoms need to develop within a specific time window to qualify as acute transverse myelitis. The formal criteria require progression from first symptoms to the worst point (called “nadir”) between 4 hours and 21 days. In practice, about half of patients reach their worst symptoms within the first week, and another third peak between 8 and 21 days. A small group, around 4%, deteriorates within just hours.
What the MRI Shows
An MRI of the spinal cord is the most important imaging test. Doctors look for areas of abnormal signal on T2-weighted sequences, which appear as bright spots where healthy cord tissue should look darker. The most sensitive MRI techniques for catching these lesions are specific sequences called STIR and T2-weighted fast spin-echo.
The length and pattern of the lesion on MRI carry significant diagnostic weight. There are three main patterns:
- Acute complete transverse myelitis: A single lesion spanning one or two vertebral segments, affecting the full thickness of the cord or concentrated in its center.
- Acute partial transverse myelitis: Also one to two segments long, but only involving a small portion of the cord’s cross-section.
- Longitudinally extensive transverse myelitis: A lesion stretching across three or more vertebral segments, typically involving the central cord over more than two-thirds of its width.
These distinctions matter because they point to different underlying causes. A short lesion is more consistent with multiple sclerosis, while a longitudinally extensive lesion raises suspicion for neuromyelitis optica spectrum disorder (NMOSD) or MOG antibody disease (MOGAD).
Gadolinium contrast dye is also given during the MRI. Enhancement (bright areas after contrast injection) indicates active inflammation and appears in roughly one-third to one-half of idiopathic cases. The enhancement pattern can be nodular, patchy, peripheral, or diffuse, and different patterns offer clues about the cause. For instance, ring-like or “cloud-like” enhancement is more typical of NMOSD, while ring-like or homogeneous enhancement suggests MOGAD.
Spinal Fluid Analysis
A lumbar puncture (spinal tap) provides cerebrospinal fluid that helps confirm inflammation and narrow down the cause. Doctors evaluate several markers in the fluid.
White blood cell count is a key indicator. Normal spinal fluid contains very few white cells, so anything above 5 cells per microliter is considered elevated. In transverse myelitis associated with MOG antibodies, for example, over half of spinal fluid samples show elevated white cells, with a typical count around 40 cells per microliter, though counts can range up to 256. Marked elevation above 100 cells is less common, appearing in about 11% of samples.
Protein levels in the fluid also matter. A total protein above 45 mg/dL is considered elevated and suggests inflammation or a disrupted barrier between the blood and the spinal fluid. About 22% of samples in one large study showed elevated protein.
Oligoclonal bands are another finding doctors check for. These are specific immune proteins that, when found only in spinal fluid and not in blood, suggest the immune system is active within the central nervous system. They appear in fewer than 10% of MOGAD cases and under 20% of NMOSD cases, but are far more common in multiple sclerosis. Their presence or absence helps distinguish between these conditions.
Blood Antibody Tests
Two antibody tests have become central to the diagnostic workup because they can identify the specific disease driving the spinal cord inflammation.
The aquaporin-4 antibody (AQP4) test detects antibodies that target a water channel protein on brain and spinal cord cells. A positive result is highly specific for NMOSD. This antibody can be detected through several lab methods, including immunofluorescence on cells that express the target protein, flow cytometry, and other specialized assays. Testing for AQP4 is now standard when someone presents with transverse myelitis, particularly when the MRI shows a longitudinally extensive lesion.
The MOG-IgG antibody test identifies a different antibody that targets a protein on the outer surface of the myelin sheath. A positive result points to MOGAD, which tends to have a more favorable long-term outcome than AQP4-positive NMOSD. In studies comparing the two, patients with MOG antibody-related transverse myelitis had lower disability scores on average than those with AQP4 antibody disease. Serum (blood) testing for MOG-IgG is more reliable than spinal fluid testing.
If both antibody tests come back negative and no other cause is identified, the diagnosis is classified as idiopathic transverse myelitis, meaning the inflammation happened without an identifiable underlying disease.
Ruling Out Other Conditions
A critical part of diagnosing transverse myelitis is excluding conditions that can mimic it. The MRI must show no evidence of a compressive cause like a herniated disc, tumor, or abscess pressing on the cord. Beyond compression, the list of conditions that need to be considered is long: multiple sclerosis, NMOSD, MOGAD, lupus-related myelitis, neurosarcoidosis, spinal cord stroke (ischemic myelopathy), infections, cancer-related (paraneoplastic) myelopathy, and metabolic causes like vitamin B12 deficiency.
Specific imaging clues help narrow things down. A lesion confined to the gray matter of the cord, visible as a characteristic “H sign” on cross-sectional MRI, favors MOGAD over MS or NMOSD. Involvement of the conus medullaris (the tapered bottom end of the spinal cord) is seen in about 26% of MOGAD cases but only around 1% of MS cases, making it a useful distinguishing feature. Certain clinical symptoms also help: area postrema syndrome (intractable nausea and vomiting) suggests NMOSD, while sphincter dysfunction early in the course is more common in MOGAD.
The Formal Diagnostic Criteria
A working group established standardized criteria to ensure consistent diagnosis across medical centers. The three most important requirements are:
- Sensory, motor, or autonomic dysfunction that clearly originates from the spinal cord
- T2 hyperintense signal changes on MRI confirming a spinal cord lesion
- No compressive lesion on imaging that could explain the symptoms
Supporting criteria include bilateral signs or symptoms and a clearly defined sensory level on exam. To confirm inflammation specifically, the criteria require evidence of either gadolinium enhancement on MRI, elevated white blood cells in spinal fluid, or an elevated IgG index (a measure of immune activity in the central nervous system). If none of these inflammatory markers are present, the diagnosis is reconsidered or the patient is re-evaluated after 2 to 7 days to see if they develop.
The entire diagnostic workup typically happens over a matter of days during a hospital stay, since transverse myelitis is treated as a neurological emergency. Treatment often begins before all test results are back, particularly if the clinical picture and MRI are strongly suggestive, because early intervention improves outcomes.