Radiologically isolated syndrome (RIS) is defined by MRI findings suggestive of multiple sclerosis (MS) in asymptomatic ("clinically silent") 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 MS (as defined by the 2010 McDonald criteria) in MRI studies performed for other indications than demyelinating disorders is referred to as RIS. Development of neurological symptoms in patients with RIS is called conversion.
While the phenomenon of asymptomatic, subclinical or clinically silent disease state of MS incidentally discovered on autopsy and later imaging studies has long been known, the extensive availability of MRI has lead 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 the incidental nature, RIS is the most common type of asymptomatic MS 3. One large retrospective cohort study stated prevalence as low as 0,05% 4. 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 conversion rate roughly equates 33% per 5 year period, a significant number of patients will not subsequently develop MS.
Due to absence of clear risk factors defining clinical conversion and lack of current evidence usually no treatment is initiated.
- primary demyelinating disorders
- clinically isolated syndrome (CIS)
- radiologically isolated syndrome (RIS)
- multiple sclerosis (MS)
- neuromyelitis optica (NMO) (Devic disease)
- acute disseminated encephalomyelitis (ADEM) and acute haemorrhagic encephalomyelitis (AHEM)
- tumefactive demyelinating lesions
- transverse myelitis
- chronic inflammatory demyelinating polyneuropathy (CIDP)
- Guillain-Barre Syndrome (GBS)
- primary demyelinating disorders
- 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