Most patients presenting with disabling myelopathy will have an abnormal MRI spine at presentation with pathognomonic radiological changes that typically clinch the diagnosis, ensure timely treatment and expediting recovery. However, in some patients with disabling myelopathy the initial MRI scan is normal, potentially delaying diagnosis and treatment. Fortunately scan-negative myelopathy is rare (Wong et al, 2008). In this scenario, somatosensory evoked evoked potentials (SSEPs) and motor evoked potentials (MEPs) could provide important diagnostic information. However, the literature on MEPs/SSEPs in scan-negative myelopathy is sparse.

We reviewed the results of neurophysiological investigations in five patients who presented between 2021 and 2023 with scan-negative myelopathy to the Royal Victoria Infirmary, Newcastle-upon-Tyne.

Patients were aged between 31 and 64 years, 4 male and 1 female. The clinical presentation ranged from symptoms of anaesthesia in the lower limbs and urinary retention to progressive tetraparesis with a thoracic sensory level and upper motor neuron signs. The initial MRI spine was reported as normal in all patients. The results of routine blood tests and CSF analysis were also normal.

SSEPs were absent from the lower limbs, consistent with significant myelopathy affecting central somatosensory pathways (n=2). In one patient, SSEP central conduction time were increased in the upper limbs and absent from the lower limbs, consistent with myelopathy affecting central somatosensory pathways from both lower and upper limbs. In one patient, SSEPs were within acceptable limits. MEPs were abnormal in all patients (n=5), identifying unilateral (n=1), or bilateral lower limb (n=1) abnormalities, or changes consistent with significant myelopathy affecting corticospinal projections to cervical and lumbosacral levels (n=3).

In two patients, when the MRI spine was repeated 2-3 months after symptom onset, this revealed increased signal in the cord, compatible with myelopathy.

Four patients received immunossupressive therapies, including intravenous methylprednisolone, rituximab and plasma exchange. This was associated with clinical stabilization in one patient, and significant improvement in the remaining patients.

In one patient, myelopathy was caused by high-voltage electrical injury but in all other cases, whilst the presumptive diagnosis was “inflammatory myelopathy” no clear aetiology was identified.

These case series illustrates the utility of evoked potentials in the diagnosis of MRI-negative myelopathy. Confirmation of myelopathy through evoked potentials can have an impact on the patient, confirming the diagnosis, expediting appropriate treatment, and guiding prognostication.