Case series: Immune checkpoint inhibitor-induced transverse myelitis.

Introduction: Increasing implementation of the highly efficacious immune checkpoint inhibitors (ICIs) has raised awareness of their various complications in the form of immune-related adverse events (irAEs). Transverse myelitis following ICIs is thought to be a rare but serious neurologic irAE and knowledge is limited about this distinct clinical entity. Cases: We describe four patients across three tertiary centers in Australia with ICI-induced transverse myelitis. Three patients had a diagnosis of stage III-IV melanoma treated with nivolumab and one patient had stage IV non-small cell lung cancer treated with pembrolizumab. All patients had longitudinally extensive transverse myelitis on magnetic resonance imaging (MRI) spine and clinical presentation was accompanied by inflammatory cerebrospinal fluid (CSF) findings. Half of our cohort had received spinal radiotherapy, with the areas of transverse myelitis extending beyond the level of previous radiation field. Inflammatory changes on neuroimaging did not extend to the brain parenchyma or caudal nerve roots, except for one case involving the conus medullaris. All patients received high dose glucocorticoids as first-line therapy, however the majority relapsed or had a refractory state (3/4) despite this, requiring escalation of their immunomodulation, with either induction intravenous immunoglobulin (IVIg) or plasmapheresis. Patients in our cohort who relapsed had a poorer outcome with more severe disability and reduced functional independence following resolution of their myelitis. Two patients had no progression of their malignancy and two patients had malignancy progression. Of the three patients who survived, two had resolution of their neurological symptoms and one remained symptomatic. Conclusion: We propose that prompt intensive immunomodulation is favored for patients with ICI-transverse myelitis in an attempt to reduce associated significant morbidity and mortality. Furthermore, there is a significant risk of relapse following cessation of immunomodulatory therapy. We suggest one treatment approach of IVMP and induction IVIg for all patients presenting with ICI-induced transverse myelitis based on such findings. With the increasing use of ICIs across oncology, further studies are required to explore this neurological phenomenon in greater detail to help establish management consensus guidelines.

Diagnosis, differential diagnosis and misdiagnosis of Susac syndrome.

BACKGROUND AND PURPOSE: Susac syndrome (SuS) is an inflammatory condition of the brain, eye and ear. Diagnosis can be challenging, and misdiagnosis is common. METHODS: This is a retrospective review of the medical records of 32 adult patients from an Australasian cohort of SuS patients. RESULTS: An alternative diagnosis prior to SuS was made in 30 patients (94%) with seven patients receiving two or more diagnoses. The median time to diagnosis of SuS was 3 months (range 0.5-100 months). The commonest misdiagnoses were migraine in 10 patients (31%), cerebral vasculitis in six (19%), multiple sclerosis in five (16%) and stroke in five (16%). Twenty-two patients were treated for alternative diagnoses, 10 of whom had further clinical manifestations prior to SuS diagnosis. At presentation seven patients (22%) met criteria for definite SuS, 19 (59%) for probable SuS and six (19%) for possible SuS. Six patients (19%) presented with brain-eye-ear involvement, 14 with brain-ear (44%), six with brain-eye (19%) and six (19%) with only brain involvement. In patients with the complete triad of symptoms the median delay to diagnosis was 3 months (range 1-9 months) compared to 5.25 months (range 0.5-100 months) for patients with encephalopathy and ocular symptoms at presentation. CONCLUSIONS: Susac syndrome patients are frequently misdiagnosed at initial presentation, despite many having symptoms or radiological features that are red flags for the diagnosis. Delayed diagnosis can lead to patient morbidity. The varied ways in which SuS can present, and clinician failure to consider or recognize SuS, appear to be the main factors leading to misdiagnosis.

Response to treatment in NMOSD: the Australasian experience.

BACKGROUND: Neuromyelitis optica spectrum disorder (NMOSD) is associated with significant morbidity and mortality. Several therapies have been recommended for NMOSD and more recently clinical trials have demonstrated efficacy for three monoclonal antibody therapies. We present a retrospective observational study of treatment response in NMOSD. METHODS: This was a retrospective, unblinded, observational study of treatment efficacy for rituximab and traditional immunosuppressive therapy in patients with AQP4 antibody positive NMOSD. Treatment efficacy was assessed using annualised relapse rates (ARR), time to first relapse and expanded disability status scale (EDSS) scores. RESULTS: Complete relapse and treatment data were available for 43/68 (63%) of AQP4 antibody positive NMOSD cases covering 74 episodes of treatment. In a time to first relapse analysis rituximab showed a risk ratio of 0.23 (95% CI 0.08 - 0.65) when compared with no treatment and there was a non-significant reduction in ARR of 35% compared to pre-treatment. ß-interferon (p = 0.0002) and cyclophosphamide (p = 0.0034) were associated with an increased ARR compared to pre-treatment. Rituximab (median 4.0 [range 0.0 - 7.0]; p = 0.042) and traditional immunosuppressive therapy (median 4.0 [range 0.0 - 8.0]; p = 0.016) were associated with a lower final EDSS compared to ß-interferon (median 6.0 [range 4.0 - 7.5]). CONCLUSIONS: These data provide additional support for the use of rituximab in preference to traditional immunosuppressive agents and MS disease modifying therapies as first line treatment of NMOSD.

Multiple Sclerosis: Microglia, Monocytes, and Macrophage-Mediated Demyelination.

This study examined the roles of microglia and monocytes in myelin destruction in patients with early multiple sclerosis (MS). Twenty-two cases were studied; the clinical duration was <9 weeks in 10 cases. Twenty myeloid cell subtypes or categories were identified including 2 cell types not known previously to occur in demyelinating diseases. Commencing myelin breakdown in plaques and in perivascular and subpial tissues occurred in the immediate presence of infiltrating monocytes and was effected by a homogeneous population of IgG-positive Fc receptor-bearing early phagocytes interacting with abnormal myelin. Oligodendrocyte apoptosis was observed in intact myelinated tissue bordering areas of active demyelination. Capillaries in the cerebral cortex plugged by large numbers of monocytes were common in acute cases of MS and in a patient with a neuromyelitis optica variant and extreme systemic recruitment of monocytes. In an MS patient with progressive disease, microglial nodules centered on MHC-II-positive capillaries plugged by monocytes were present in the cerebral cortex. This constitutes a new gray matter lesion in MS.

Interferon-ß Is Less Effective Than Other Drugs in Controlling the Rate of Retinal Ganglion Cell Loss in MS.

OBJECTIVE: To investigate the association between disease-modifying therapies (DMTs) and the rate of progressive retinal ganglion cell (RGC) and nerve fiber loss in MS. METHODS: One hundred five relapsing-remitting patients with MS were followed annually for a median of 4.0 years using optical coherence tomography. Twenty-five healthy subjects were also included as normal controls. The rates of global peripapillary retinal nerve fiber layer (pRNFL), temporal RNFL (tRNFL), and ganglion cell inner plexiform layer (GCIPL) thinning were analyzed according to DMT type using a linear mixed-effects model. Optic radiation lesion volume was measured on brain MRI and included as a covariate to minimize the effects of retrograde transsynaptic degeneration. RESULTS: The annual rates of RNFL and GCIPL thinning were higher in patients treated with "platform" therapies (interferon-ß and glatiramer acetate) compared with DMTs of higher clinical efficacy (including fingolimod, dimethyl fumarate, natalizumab, alemtuzumab, rituximab, and ocrelizumab) (difference = -0.22 µm/y, p = 0.02 for pRNFL; difference = -0.34 µm/y, p = 0.009 for tRNFL; and difference = -0.16 µm/y, p = 0.005 for GCIPL). Based on an analysis of individual treatments (interferon-ß, glatiramer acetate, fingolimod, and natalizumab), interferon-ß was associated with inferior RGC preservation, relative to the other drugs. No effect difference was found between glatiramer acetate, fingolimod, and natalizumab. CONCLUSIONS: Progressive loss of RGCs in patients with MS is more pronounced in patients treated with interferon-ß than other DMTs. This finding may have implications for DMT selection in MS. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that for patients with MS, treatment with interferon-ß compared with other DMTs leads to a more pronounced rate of retinal ganglion cell loss.

The neuro-otology of Susac syndrome.

OBJECTIVE: We characterised the clinical and neuro-otological characteristics of patients with Susac syndrome. METHODS: The medical records of 30 patients with Susac syndrome were reviewed for details of their clinical presentation and course, neuro-otological symptoms, investigation results including audiology and vestibular function tests, treatment and outcomes. RESULTS: Our findings demonstrate that 29 of our 30 patients with Susac syndrome developed neuro-otological symptoms such as hearing loss, disequilibrium, tinnitus or vertigo during their disease course. Hearing loss was the most common neuro-otological symptom occurring in 93% of patients. A rising configuration of low-frequency greater than the high-frequency sensorineural hearing loss was the most characteristic finding on audiological testing (37% of reviewed audiograms). Disproportionately poor speech discrimination was identified in 20% of cases, and one case demonstrated a retrocochlear pattern on electrophysiological testing. Four patients required hearing aids and a further two patients required a cochlear implant due to severe hearing loss. Two out of two treated patients had improvements in hearing after the prompt administration of corticosteroids, indicating the potential for recoverable hearing loss if relapses are treated early. Effects on vestibular function were variable in ten patients who were tested, with most showing preservation of function despite significant hearing loss. CONCLUSIONS: Neuro-otological symptoms in Susac syndrome are almost universal. In the correct clinical context, a rising configuration of low to high-frequency sensorineural hearing loss should prompt consideration of Susac syndrome. Treatment of inner ear symptoms in Susac syndrome requires further research as early immunotherapy may be beneficial.

The Successful Use of Infliximab in a Relapsing Case of Susac's Syndrome.

Susac's syndrome is a rare and debilitating disease characterized by the triad of encephalopathy, branch retinal artery occlusions, and sensorineural hearing loss. All manifestations may not be clinically apparent at presentation resulting in delayed diagnosis. Early recognition of the syndrome may prevent disease sequelae such as permanent cognitive, visual, and hearing loss. We present such a case of Susac's syndrome that was also refractory to conventionally prescribed combination of immunosuppressive treatments including high-dose potent corticosteroids, intravenous cyclophosphamide, methotrexate, plasma exchange, rituximab, and mycophenolate. His disease was stabilized with infliximab in combination with a tapering course of low-dose prednisone. After 2 years of remission with TNF treatment, consideration is being given to ceasing therapy. He has the sequelae of bilateral sensorineural hearing loss but no visual impairment or cognitive deficits on follow-up with neuropsychometric testing. This is the first case report to our knowledge of the successful use of infliximab for a patient with Susac's syndrome that was necessary following treatment with cyclophosphamide and then rituximab.

AQP4 Antibody Assay Sensitivity Comparison in the Era of the 2015 Diagnostic Criteria for NMOSD.

We have compared five different assays for antibodies to aquaporin-4 in 181 cases of suspected Neuromyelitis optica spectrum disorders (NMOSD) and 253 controls to assess their relative utility. As part of a clinically-based survey of NMOSD in Australia and New Zealand, cases of suspected NMOSD were referred from 23 centers. Clinical details and magnetic imaging were reviewed and used to apply the 2015 IPND diagnostic criteria. In addition, 101 age- and sex-matched patients with multiple sclerosis were referred. Other inflammatory disease (n = 49) and healthy controls (n = 103) were also recruited. Samples from all participants were tested using tissue-based indirect immunofluorescence assays and a subset were tested using four additional ELISA and cell-based assays. Antibodies to myelin oligodendrocyte glycoprotein (MOG) were also assayed. All aquaporin-4 antibody assays proved to be highly specific. Sensitivities ranged from 60 to 94%, with cell-based assays having the highest sensitivity. Antibodies to MOG were detected in 8/79 (10%) of the residual suspected cases of NMOSD. Under the 2015 IPND diagnostic criteria for NMOSD, cell-based assays for aquaporin-4 are sensitive and highly specific, performing better than tissue-based and ELISA assays. A fixed cell-based assay showed near-identical results to a live-cell based assay. Antibodies to MOG account for only a small number of suspected cases.

Multiple sclerosis: Serum anti-CNS autoantibodies.

BACKGROUND: It is uncertain whether there are autoantibodies detectable by indirect immunofluorescence in the serum of patients with multiple sclerosis (MS). OBJECTIVE: To determine whether there are anti-central nervous system (CNS) autoantibodies detectable by indirect immunofluorescence in the serum of MS patients. METHODS: Sera and in some cases cerebrospinal fluid from 106 patients with multiple sclerosis, 156 patients with other neurological diseases, and 70 healthy control subjects were examined by indirect immunofluorescence using cryostat sections of rat cerebrum fixed by perfusion with paraformaldehyde. RESULTS: Autoantibodies were detected that recognized more than 30 neuronal, glial, and mesodermal structures in 28 of 106 MS cases. Most were also detected in patients with other related and unrelated neurological diseases and several were also found in healthy controls. Novel anti-CNS autoantibodies recognizing particular sets of interneurons were detected in both normal controls and in subjects with CNS diseases. INTERPRETATION: Serum anti-CNS autoantibodies of diverse specificities are common in MS patients. The same anti-CNS autoantibodies are not uncommon in patients with other neurological diseases. The findings provide no support for the proposition that myelin breakdown in MS is caused by exposure of intact myelin sheaths or oligodendrocytes to a pathogenic serum anti-myelin or anti-oligodendrocyte autoantibody.

Fibrosis of the Choroid Plexus Filtration Membrane.

We report a previously undescribed inflammatory lesion consisting of deposition of activated complement (C3d and C9neo) in association with major histocompatibility complex type II (MHC2)-positive activated microglia in choroid plexus villi exhibiting classical fibrous thickening of the pericapillary filtration membrane. The proportion of villi affected ranged from 5% to 90% in 56 adult subjects with diseases of the CNS and 11 subjects with no preexisting disease of the CNS. In 3 of the 4 children studied, 2% or less of examined villi showed stromal thickening, complement deposition, and the presence of MHC2-positive microglia; in adults, the proportion of villi affected increased with age. Other features of the lesion included loss of capillaries and failure by macrophages to clear extracellular particulate electron-dense material by clathrin-mediated phagocytosis. This choroid plexus lesion may relate pathogenetically to age-related macular degeneration and to Alzheimer disease, 2 other conditions with no known risk factors other than increasing age. All 3 conditions are characterized by the presence of damaged capillaries, inflammatory extracellular aggregates of mixed molecular composition and defective clearance of the deposits by macrophages.

Radiological differentiation of optic neuritis with myelin oligodendrocyte glycoprotein antibodies, aquaporin-4 antibodies, and multiple sclerosis.

BACKGROUND: Recognizing the cause of optic neuritis (ON) affects treatment decisions and visual outcomes. OBJECTIVE: We aimed to define radiological features of first-episode demyelinating ON. METHODS: We performed blinded radiological assessment of 50 patients presenting with first-episode myelin oligodendrocyte glycoprotein (MOG) antibody-associated ON (MOG-ON; n=19), aquaporin-4 (AQP4) antibody-associated ON (AQP4-ON; n=11), multiple sclerosis (MS)-associated ON (MS-ON; n=13), and unclassified ON (n=7). RESULTS: Bilateral involvement was more common in MOG-ON and AQP4-ON than MS-ON (84% vs. 82% vs. 23%), optic nerve head swelling was more common in MOG-ON (53% vs. 9% vs. 0%), chiasmal involvement was more common in AQP4-ON (5% vs. 64% vs. 15%), and bilateral optic tract involvement was more common in AQP4-ON (0% vs. 45% vs. 0%). Retrobulbar involvement was more common in MOG-ON, whereas intracranial involvement was more common in AQP4-ON. MOG-ON and AQP4-ON had longer lesion lengths than MS-ON. The combination of two predictors, the absence of magnetic resonance imaging brain abnormalities and a higher lesion extent score, showed a good ability to discriminate between an autoantibody-associated ON (MOG or AQP4) and MS. AQP4-ON more frequently had severe and sustained visual impairment. CONCLUSION: MOG-ON and AQP4-ON are more commonly bilateral and longitudinally extensive. MOG-ON tends to involve the anterior optic pathway, whereas AQP4-ON the posterior optic pathway.

Antibodies to myelin oligodendrocyte glycoprotein in bilateral and recurrent optic neuritis.

OBJECTIVE: We examined a cohort of adults with aquaporin-4 (AQP4) antibody-negative neuromyelitis optica/neuromyelitis optica spectrum disorder (NMO/NMOSD) for antibodies to myelin oligodendrocyte glycoprotein (MOG). METHODS: We performed a flow cytometry cell-based assay using live human lentivirus-transduced cells expressing full-length surface MOG. Serum was tested in 23 AQP4 antibody-negative NMO/NMOSD patients with bilateral and/or recurrent optic neuritis (BON, n = 11), longitudinally extensive transverse myelitis (LETM, n = 10), and sequential BON and LETM (n = 2), as well as in patients with multiple sclerosis (MS, n = 76) and controls (n = 52). RESULTS: MOG antibodies were detected in 9/23 AQP4 antibody-negative patients with NMO/NMOSD, compared to 1/76 patients with MS and 0/52 controls (p < 0.001). MOG antibodies were detected in 8/11 patients with BON, 0/10 patients with LETM, and 1/2 patients with sequential BON and LETM. Six of 9 MOG antibody-positive patients had a relapsing course. MOG antibody-positive patients had prominent optic disc swelling and were more likely to have a rapid response to steroid therapy and relapse on steroid cessation than MOG antibody-negative patients (p = 0.034 and p = 0.029, respectively). While 8/9 MOG antibody-positive patients had good follow-up visual acuity, one experienced sustained visual impairment, 3 had retinal nerve fiber layer thinning, and one had residual spinal disability. CONCLUSIONS: MOG antibodies have a strong association with BON and may be a useful clinical biomarker. MOG antibody-associated BON is a relapsing disorder that is frequently steroid responsive and often steroid dependent. Failure to recognize the disorder early and institute immunotherapy promptly may be associated with sustained impairment. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that MOG antibodies are associated with AQP4 antibody-negative BON (sensitivity 69%, 95% confidence interval [CI] 42%-87%; specificity 99%, 95% CI 93.7%-99.8%).

Oligodendrocytes and the early multiple sclerosis lesion.

There is little agreement among neuropathologists regarding the timing and nature of oligodendrocyte loss in multiple sclerosis (MS). This review describes changes that accompany acute oligodendrocyte loss in new lesions. Included is a description of the immunopathology of new lesions in 23 severe early cases selected from a bank of 300 MS autopsies. Oligodendrocytes in prephagocytic lesions exhibit cytopathic changes that include apoptosis of oligodendrocytes immunoreactive for caspase 3, phagocytosis of apoptotic oligodendrocytes, swelling of cells with abnormal nuclei, complement deposition, and lysis. These are nonspecific changes that provide no clue as to the cause of oligodendrocyte injury. Associated changes include the presence of enlarged immunoglobulin (IgG)(+) microglia and early macrophages, the presence nearby of a focus of inflammatory demyelination, an open blood-brain barrier, and the presence of rare CD8 T cells. Myelin contacted by IgG(+) macrophages is immunoreactive for complement but not for IgG. It is likely that macrophage activity in evolving white and gray matter plaques is scavenging activity directed at nonvital myelin secondary to oligodendrocytes loss. One feature of MS that is not understood is the extraordinarily close resemblance the disease shows pathologically to neuromyelitis optica (NMO), including that demyelination in both is secondary to a loss of caspase 3-positive apoptotic oligodendrocytes. These similarities raise the possibility that like NMO, MS is an autoimmune disease in which oligodendrocyte apoptosis is determined by injury to some other glial or mesenchymal component.

Neuromyelitis optica: a demyelinating disease characterized by acute destruction and regeneration of perivascular astrocytes.

BACKGROUND: A serum antibody directed against astrocytes is present in a high proportion of patients with neuromyelitis optica (NMO). The pathogenicity of the antibody is uncertain because no consistent astrocyte lesion is known to occur in NMO. OBJECTIVE: To determine whether there is an astrocyte lesion in NMO and if this differs from astrocyte changes in multiple sclerosis (MS). METHODS: Astrocyte pathology in early (still-myelinated) lesions and subacute NMO and MS lesions was examined immunohistochemically and in sections stained for astrocytes using routine histological techniques. RESULTS: Demyelination in early NMO lesions is accompanied by oligodendrocyte apoptosis in a pattern identical to that seen in MS and this is preceded by an abrupt destruction of perivascular astrocytes. Reparative astrogliosis is effected by a population of unipolar, new astrocytes. Evidence of a different type of astrocyte lesion was found in MS. DISCUSSION: The findings add to experimental evidence that the antibody is pathogenic. They also raise the possibility that demyelination in MS may be a bystander effect of an astrocyte lesion, i.e. that MS is not a disease primarily of myelin and oligodendrocytes.

Multiple sclerosis: distribution of inflammatory cells in newly forming lesions.

OBJECTIVE: CD4 T-cell-dependent macrophage activation directed against a myelin or oligodendrocyte antigen is generally thought to be the mechanism causing myelin destruction in multiple sclerosis (MS). However, areas within expanding MS lesions may exhibit prominent oligodendrocyte loss and apoptosis in the absence of infiltrating lymphocytes. The present study was designed to further investigate the inflammatory profile of different regions within rapidly expanding MS lesions. METHODS: Twenty-six active lesions from 11 patients with early MS were serially sectioned and immunostained for T and B cells, plasma cells, ramified microglia, macrophages, monocytes, and CD209-positive dendritic cells. Cell counts were compared in prephagocytic, phagocytic, and immediately postphagocytic areas. RESULTS: Parenchymal T and B cells were largely absent in areas of initial oligodendrocyte loss and in areas of degenerate and dead myelin infiltrated by myelin phagocytes. In contrast, trailing areas of complete demyelination packed with lipid macrophages, and, in some lesions, regenerating oligodendrocytes, showed large numbers of T cells, B cells, and immunoglobulin G (IgG)-positive plasma cells. Lesions in 2 exceptionally early cases contained relatively few T and B cells, and no IgG-positive plasma cells. INTERPRETATION: Early loss of oligodendrocytes is a prominent feature in tissue bordering rapidly expanding MS lesions. Macrophage activity is largely an innate scavenging response to the presence of degenerate and dead myelin. Adaptive immune activity involving T and B cells is conspicuous chiefly in recently demyelinated tissue, which may show signs of oligodendrocyte regeneration. The findings suggest that plaque formation has some basis other than destructive cell-mediated immunity directed against a myelin or oligodendrocyte antigen.

Immunoglobulins and complement in postmortem multiple sclerosis tissue.

OBJECTIVE: To identify evidence of a discrete, specific immune response in multiple sclerosis (MS) by analyzing the distribution of immunoglobulins and complement in tissue derived from cases of MS, and from control inflammatory white matter diseases known to express viral and autoantigens in the brain and spinal cord. METHODS: Autopsy tissue from 25 MS patients and 24 patients with other neurological diseases was examined immunohistochemically for immunoglobulins and activated complement (C3d and C9neo). RESULTS: In tissue remote from focal lesions in MS and other neurological diseases, IgG was detected in many normal structures but not in myelin or ramified microglia. Disrupted myelin in areas of active myelin breakdown and in phagocytes stained positively for C3d and C9neo, and equivocally for IgG in MS and all other neurological diseases examined, including ischemic infarcts. Disease-specific deposits of IgG or complement were detected in virus-infected cells in progressive multifocal leukoencephalopathy, subacute sclerosing panencephalitis, and cytomegalovirus encephalitis; in glial-limiting membranes in neuromyelitis optica; and in senile plaques in Alzheimer's dementia. Specific to MS were unusual microglial nodules containing short, linear deposits of activated complement (C3d) on partly demyelinated axons located in normal-appearing periplaque white matter. INTERPRETATION: IgG and complement immunostaining of disrupted myelin in MS lesions, frequently cited as an indication of pathogenic anti-myelin antibodies, is a nonspecific feature that cannot be interpreted as evidence of a distinct pathogenesis or serve to define particular variants of the disease. The unusual microglial nodules described in this study may constitute a specific biomarker with pathogenetic significance in MS.

Multiple sclerosis in Tayside, Scotland: detection of clusters using a spatial scan statistic.

Debate continues over the relative importance of genetic factors over infectious agents in the aetiology of multiple sclerosis (MS). Detection of clusters of MS in space and time in the Tayside region of Scotland, UK would provide valuable evidence for the movement of infectious agents into a genetically susceptible population. A spatial scan statistic was used to detect, locate and provide a robust statistical test of any clusters found, without prior knowledge of their location or size. This was applied to a population-based MS register for the Tayside region of Scotland from 1970 to 1997, allowing for age at symptom onset, gender, population density and social deprivation. There were a total of 772 cases during the study period; an annual incidence of 72 per 100000. The mean age of symptom onset was 35.7 (SD = 10.5) and 73.8% of cases were women. There was a general increase in cases over time probably reflecting gradually better detection and diagnosis. There was a peak around the mid-1990s and some evidence of periodicity. There was a highly significant temporal cluster between 1982 and 1995 (P = 0.002) for the whole region. Additionally, a significant spatial cluster for the time period 1993-1995 was found centred in the rural area south-west of Perth (P=0.016). Significant temporal and spatial-temporal clusters are consistent with exogenous factors contributing to the distribution of MS in Tayside, Scotland.