Neuromyelitis optica (or Devic's disease) is characterized by confluent demyelination in both optic nerves and the chiasm, together with equally severe spinal cord damage. These sites can be affected simultaneously or sequentially and in either order, events usually being separated by several weeks or months. The syndrome may complicate collagen vascular disease, Behçet's disease, and acute disseminated encephalomyelitis (Section 29.3.1). Opinions differ about whether this form of demyelination is usually an atypical manifestation of multiple sclerosis. Similar difficulties arise in distinguishing vasculitic from demyelinating cases, as with other examples of post-infectious inflammatory disease affecting the central nervous system. The fact that demyelinating disease more often follows the Devic pattern in Japanese, where multiple sclerosis is rare, and some series of patients with neuromyelitis optica studied in northern Europe have shown a very low conversion rate to multiple sclerosis, suggesting that they are separate disorders. Conversely, the experience of many clinicians is that the majority of patients with the combination of bilateral simultaneous optic neuritis and transverse myelitis show manifestations of demyelination arising from other parts of the central nervous system and experience multiple events with time. That has usually been our experience of these rare but tragic cases in whom a series of aggressive episodes of demyelination produce severe morbidity and threaten life.
The issue is not settled. Mandler et al. (1993) make a strong case for a different aetiology; they describe eight patients, three of whom had optic neuritis and myelitis simultaneously, and the remainder at intervals of 4–24 months. Cerebral magnetic resonance imaging in three cases examined showed no brain lesions. Imaging of the spinal cord showed swelling and cavitation. Oligoclonal bands in the CSF were found transiently in one case and were absent in six. These cases had a high mortality. Silber et al. (1990) reported 11 cases of Devic's disease occurring in the Cape coloured population of South Africa. In six, the neurological disorder started soon after the development of pulmonary tuberculosis, and optic nerve damage preceded the spinal lesion, both of which had a poor outcome. The short-term mortality was 25 per cent. Others have reported the occurrence of acute necrotizing myelitis in association with tuberculosis. Taken with the pleocytosis and glycorrhachic changes that often occur in cerebrospinal fluid, it is not surprising that these patients are usually treated with anti-tuberculous therapy, at least until bacteriological results are available.
In contrast to these specific causes of the Devic syndrome, O'Riordan et al. (1996) retrospectively reviewed 12 patients from the UK, of whom more than 50 per cent were Asian or African, taking as their definition cases with a rapidly evolving complete transverse myelitis, uni- or bi-lateral optic neuropathy, and no involvement outside these sites. Antecedent causes or coexistent illnesses were present in five. The myelopathy was often relapsing and functional recovery poor despite treatment with corticosteroids; bilateral involvement with recurrence and poor prognosis also characterized the optic neuropathy. Thus, the patients in this series typically had a multiphasic illness. The spinal fluid was usually normal without oligoclonal bands and the cellular reaction involved polymorphonuclear cells more than lymphocytes. When cerebral white matter abnormalities were present (approximately 50 per cent of patients), these tended to be frontotemporal and the spinal cord was often diffusely swollen with extensive or multiple T2-weighted lesions. The most recent and largest series of 71 patients observed over 43 years at the Mayo Clinic adopts strict diagnostic criteria relating to the bilaterality of optic nerve involvement and the interval between defining events, but usefully demonstrates a pattern of reasonable recovery when the optic nerves and spinal cord are affected in rapid sequence, and a poor prognosis with high mortality in relapsing patients with more than the two defining episodes. As now generally recognized, the spinal lesion is long, extending over several segments, in contrast to the several short lesions which characterize spinal magnetic resonance imaging in multiple sclerosis; cerebral imaging may be normal and there is typically more pronounced pleocytosis of the cerebrospinal fluid (Wingerchuk et al. 1999).