Radiologically isolated syndrome (RIS) is defined by MRI findings meeting imaging criteria for multiple sclerosis in the brain and/or spinal cord in asymptomatic patients. Radiological progression usually occurs in approximately 66% of patients with RIS, while ~33% per 5-year-period will subsequently develop neurological symptoms 1,3.
The incidental detection of brain and/or spinal cord lesions compatible with multiple sclerosis (as defined by the dissemination in time component of the 2010 McDonald criteria) in MRI studies performed for other indications than demyelinating disorders is referred to as radiologically isolated syndrome (RIS). Development of neurological symptoms in patients with RIS is called conversion.
While the phenomenon of an asymptomatic, subclinical or clinically silent disease state of multiple sclerosis, incidentally discovered on autopsy and later imaging studies, has long been known, the extensive availability of MRI has led to a significant number of studies performed for indications other than inflammatory demyelinating disorders of the CNS, giving rise to this newly defined syndrome.
While the exact prevalence is unknown owing to its incidental nature, RIS is the most common type of asymptomatic multiple sclerosis 3. One large retrospective cohort study stated prevalence as low as 0.05% 4 or as high as 0.1-0.7% 7 depending on methodology and definitions. Prevalence might be higher in relatives to patients suffering from multiple sclerosis 6.
Treatment and prognosis
As stated above, radiological progression has been shown to occur in ~66% of patients with RIS. While the conversion rate roughly equates to 33% per 5-year-period, a significant number of patients will not subsequently develop multiple sclerosis.
Due to the absence of clear risk factors defining clinical conversion and lack of current evidence usually, no treatment is initiated.
- 1. Granberg T, Martola J, Kristoffersen-Wiberg M et-al. Radiologically isolated syndrome-incidental magnetic resonance imaging findings suggestive of multiple sclerosis, a systematic review. Mult. Scler. 2013;19 (3): 271-80. doi:10.1177/1352458512451943 - Pubmed citation
- 2. Polman CH, Reingold SC, Banwell B et-al. Diagnostic criteria for multiple sclerosis: 2010 revisions to the McDonald criteria. Ann. Neurol. 2011;69 (2): 292-302. doi:10.1002/ana.22366 - Free text at pubmed - Pubmed citation
- 3. Siva A. Asymptomatic MS. Clin Neurol Neurosurg. 2013;115 Suppl 1: S1-5. doi:10.1016/j.clineuro.2013.09.012 - Pubmed citation
- 4. Granberg T, Martola J, Aspelin P et-al. Radiologically isolated syndrome: an uncommon finding at a university clinic in a high-prevalence region for multiple sclerosis. BMJ Open. 2013;3 (11): e003531. doi:10.1136/bmjopen-2013-003531 - Free text at pubmed - Pubmed citation
- 5. Okuda DT, Siva A, Kantarci O et-al. Radiologically isolated syndrome: 5-year risk for an initial clinical event. PLoS ONE. 2014;9 (3): e90509. doi:10.1371/journal.pone.0090509 - Free text at pubmed - Pubmed citation
- 6. Gabelic T, Ramasamy DP, Weinstock-Guttman B et-al. Prevalence of radiologically isolated syndrome and white matter signal abnormalities in healthy relatives of patients with multiple sclerosis. AJNR Am J Neuroradiol. 2014;35 (1): 106-12. doi:10.3174/ajnr.A3653 - Pubmed citation
- 7. Yamout B, Al Khawajah M. Radiologically isolated syndrome and multiple sclerosis. (2017) Multiple sclerosis and related disorders. 17: 234-237. doi:10.1016/j.msard.2017.08.016 - Pubmed
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