Wallerian degeneration in spinal cord secondary to inflammatory demyelinating lesion

A 16-year-old male patient with myelitis of three years of evolution at C3–C4 level, a history of oral aphthous ulcers and cerebral thrombosis, and diagnosed with Behçet’s disease. He presented with paraesthesia and hypoesthesia in the lower extremities. He is currently being treated with Rituximab without significant sequelae.

Cervical MRI at the three-year follow-up demonstrated a confluent central lesion of the spinal cord at C3–C4 level with hyperintensity on T2WI (Figures 1 and 2), mild enhancement (Figure 3) and microhaemorrhage spot (Figure 4).

It causes hyperintensity on T2WI at the white matter columns of the spinal cord of the adjacent segments:

• Rostral, the medial lemniscus system within the dorsal columns (Figure 5) and the extrapyramidal tracts within the ventral columns (Figure 6).
• Caudal, the corticospinal tract within the lateral columns (Figure 7).
• The findings suggest changes due to Wallerian degeneration.

Background

Wallerian degeneration (WD) refers to the progressive disintegration of axons and myelin sheaths following disruption of the connection to the cell body. Classically, only anterograde degeneration was described, although there is evidence for a common mechanism in both anterograde and retrograde degeneration [1–3].

Clinical Perspective

WD is a process best known in the brain but can also affect different white matter tracts at the level of the spinal cord. The lateral corticospinal tracts (CS) are part of the efferent motor pathways. The dorsal column (DC) or the lateral spinothalamic tract (ST) both part of the afferent sensory pathways [2].

It is common in clinical practice to use imaging techniques to assess the evolution of spinal cord involvement in different pathologies that can lead to WD, the most frequent being trauma. Other non-traumatic causes include degenerative myelopathies, neoplasms, surgery and demyelinating diseases [1].

Imaging Perspective

Four stages of WD were described in the brain and are expected to be similar in the spinal cord. In early stages, evidence of acute injury has been demonstrated on DWI in less than 10 days. Hyperintense signal can be seen on T2 WI after 14 weeks in affected axons due to gliosis and increased water content. In the final stage, months or years after the injury, the hyperintense signal persists with volume loss and atrophy [4]. These are non-contrast enhancing lesions.

WD is seen fairly well-defined and symmetrical at the DC and ST cranial to the lesion site and at the CS below the level of the lesion. The length of the affected segment is proportional to the number of damaged axons. Therefore, the length is greater in the cervical region, where the axons are more tightly packed compared to the dorsal or lumbar region [4].

DTI has also demonstrated its potential to provide prognostic information [1].

Outcome

Wallerian degeneration involves an irreversible loss of neuronal function that may cause residual symptoms that do not resolve after treating the original cause.

Take Home Message / Teaching Points

Wallerian degeneration is a common but not so well-known process in the spinal cord.

The combined involvement of CS caudal to the lesion and DC and ST rostral to the lesion with preservation of the grey matter is quite specific to WD, which, in conjunction with the patient’s clinical history, can help guide the diagnosis to avoid confusion with other pathologies that it may mimic [3–5].

Written informed patient consent for publication has been obtained.