The clinical spectrum and prognosis of idiopathic acute optic neuritis: A longitudinal study in Southern Finland.

BACKGROUND

To analyse in a population-based setting the clinical features, prognostic factors, and seasonality of patients diagnosed with acute idiopathic optic neuritis (ON).

METHODS

Retrospective analysis of ophthalmological records, laboratory parameters, and magnetic resonance imaging (MRI) of patients with symptoms suggestive of ON referred to the Helsinki University Hospital (serving a population of 1.53 million in Southern Finland) were analysed between May 1, 2008 and April 14, 2012.

RESULTS

Of the 291 patients with suspected ON, 184 (63%) were diagnosed with ON (mean age 34 years, 76% females). Intravenous methylprednisolone treatment was administered in 131 (71%) patients. First ON was diagnosed in 123 patients (67%), 55 (30%) had a previous diagnosis of multiple sclerosis (MS) and two patients with their first ON were diagnosed with neuromyelitis optica. Evolution of best corrected visual acuity (BCVA) was analysed in 132 (72%) patients, who were reviewed median of 38 days after onset. Median and mean BCVAs in these reviewed patients were 0.4 and 0.2 at the time of diagnosis and 1.0 and 0.5 at the time of the review. Recovery was relatively good in the majority of patients; 82% (n = 108) had reached BCVA of ≥0.5 and 70% (n = 92) and BCVA of ≥0.8 at the time of the review, while thirteen (10%) had poor prognosis, BCVA ≤0.1 at review. Accessory clinical features included optic disc swelling (21%), colour vision impairment (75%), and pain with eye movements (65%). Relative afferent pupillary defect was abnormal in 76% of the patients with their first ON. Baseline visual acuity was most strongly associated with visual outcome at review (P < 0.001, linear regression). Optic disc swelling and the presence of lesions in the optic nerve on MRI had a more modest association with poorer recovery (P = 0.033 and P = 0.049, respectively), while age, sex, previous history of ON, and previous diagnosis of multiple sclerosis were not associated with outcome at review. Incidence of ON showed a clear seasonal pattern; there were two times more cases in April to June versus October to December (P = 0.03), confirming previous results from Sweden.

CONCLUSIONS

Our data suggest that besides baseline visual acuity, optic disc swelling and lesions in the optic nerve on MRI are associated with poorer prognosis. As in previous studies, we observed that diagnostics of ON is difficult, accessory clinical findings such as pain and RAPD are not always present. Although the diagnosis of ON is clinical, the role of MRI should be considered in differential diagnostics and in defining potential prognostic markers.