Long term MRI follow-up of patients with post infectious encephalomyelitis: evidence for a monophasic disease
Introduction
Post infectious encephalomyelitis is a central nervous system inflammatory demyelinating disorder developing acutely or subacutely in close temporal relationship to an infective illness [1], [2], [3]. It has a close resemblance to the encephalomyelitis that rarely follows vaccination. The disease is usually disseminated with a particular predilection to both optic nerves, the spinal cord, brain stem or diffuse symmetrical involvement of the basal ganglia or cerebral and cerebellar hemispheres [3], [4], [5]. There are clinical and pathological similarities between post infectious encephalomyelitis and multiple sclerosis. Both are demyelinating diseases affecting the central nervous system. However, whereas post infectious encephalomyelitis is considered a monophasic illness, multiple sclerosis is not and results in recurrent episodes disseminated in both time and place. This has obvious prognostic implications for the patient but also therapeutic considerations for the physician in view of the development of specific disease modifying therapy for multiple sclerosis [6], [7].
Clinical reports of cases of acute disseminated encephalomyelitis – defined as those patients with encephalomyelitis following a vaccination or an infective illness and sometimes including those with presentations considered atypical for multiple sclerosis highlight the difficulties in distinguishing it from MS. Follow-up suggests that the majority are indeed monophasic, but that relapsing forms may exist and some may convert to clinically definite multiple sclerosis [1], [3]. It is possible that patients with a disseminated multifocal presentation of multiple sclerosis have been included in some studies. It is also pertinent to remember that relapses of multiple sclerosis may follow infections [8]. Magnetic resonance imaging (MRI) demonstrates white matter lesions in both post infectious encephalomyelitis and multiple sclerosis which may be indistinguishable, although in some instances there are features considered more typical of one disorder than the other [4], [5]. In addition short term follow-up studies (up to 18 months) have shown partial to complete resolution of abnormalities in post infectious encephalomyelitis without new lesion formation [3], [5]. This is in contrast to multiple sclerosis in which new lesions are frequently seen on serial follow-up with or without clinical symptoms [8], [9]. It is unclear whether this short term MRI evolution is maintained in the long term and whether or not these patients have a subsequent propensity to the development of multiple sclerosis. This study was designed to answer this question in a group of patients followed prospectively and determined at presentation to have a post infectious encephalomyelitis.
Section snippets
Materials and methods
All patients presenting to The National Hospital for Neurology and Neurosurgery, Queen Square, London between 1985 and 1992 with a diagnosis of post infectious encephalomyelitis were considered for inclusion in this study. In addition 5 further patients seen at The Hospital for Sick Children, Great Ormond Street, London between 1985 and 1987, and previously the subject of a short term follow up were included [3]. This was a highly selected group followed in a prospective manner with restrictive
Results
Eleven patients were seen for follow-up after a mean duration of 8 years (3.5–11). There were 5 females and 6 males with a mean age at presentation of 21 years (4–48), 4 patients being under 10 years. Eight patients presented with clinical evidence of a multi focal neurological syndrome (cases 1–3, 6–10), one a brain stem syndrome (case 11), one a complete transverse myelitis (case 4), and, one bilateral optic neuritis (case 5). The clinical features and associated infective episode are
Discussion
The 11 patients presented in this report developed an encephalomyelitic illness in close temporal relationship to an infective episode. The infections were predominantly viral in nature. No patient experienced a relapse during a mean follow-up of 8 years. The development of a post infective encephalomyelitic illness is well recognised and closely resembles post vaccinal and experimental allergic forms [1], [2], [3], [4], [5], [10], [11], [12], [13]. Occasionally an idiopathic disturbance occurs
Acknowledgements
We would like to thank Mr David MacManus for performing the scans. The two scanners were provided by a generous grant from the Multiple Sclerosis Society of Great Britain and Northern Ireland. Dr Gomez-Anson was funded by the Spanish Ministry of Health.
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