OCT may help identify subclinical damage in longitudinally extensive transverse myelitis

This study investigated the use of OCT to measure retinal nerve fiber layer (RNFL) thickness and detect subclinical axonal loss in patients with idiopathic longitudinally extensive transverse myelitis (LETM) without previous episodes of optic neuritis. The authors report in the February 2011 issue of Arquivos de Neuro-Psiquiatria that by measuring and comparing the RNFL thickness of each quadrant and 30-degree segment of a relatively large sample of eyes, they were able to identify localized neural loss that might have remained undetected if only the average (360-degree) thickness measurements had been used. They conclude that RNFL measurements using OCT could potentially be used to identify subclinical axonal damage in patients with idiopathic LETM before episodes of optic neuritis occur.

The authors compared automated perimetry and OCT results in 26 patients (26 eyes) with longitudinally extensive transverse myelitis (LETM) without previous optic neuritis and 26 age-matched healthy controls (26 eyes). They evaluated average, quadrantic and segmental RNFL thickness in order to investigate possible occurrences of subclinical, diffuse or localized involvement of the optic nerve among the patients.

They found that the mean deviation values from perimetry were significantly lower in LETM patients than controls (P < 0.0001). RNFL measurements in the nasal quadrant and in the 3-o’clock segment also were significantly smaller in LETM eyes than in controls (P = 0.04 and P = 0.006, respectively).

The authors conclude that patients with LETM may present with localized RNFL loss, particularly on the nasal side of the optic disc, associated with slight visual field defects even in the absence of previous episodes of optic neuritis. These findings emphasize the fact that LETM patients may experience attacks of subclinical optic nerve damage that may occur as focal RNFL rather than generalized axonal loss.

However, the authors say that longitudinal studies with larger numbers of patients are required in order to fully explore the potential uses of OCT for evaluating patients with idiopathic LETM and neuromyelitis optica, with which it is strongly associated.