The first episode with focal neurological symptoms (optic neuritis or spinal cord/brainstem syndromes or others symtpoms), when diffuse typical demyelinating lesions of different ages are visible on the magnetic resonance images, allows to retain the diagnosis of multiple sclerosis (MS).
However, for some young individuals (generally with an age between 20 and 40 years), such a first clinical episode (suggesting for its presentation a demyelinating disease such as MS) might be completely isolated in time (there is no evidence of brain lesions of different ages) and in space (monofocal episode). This condition is defined as a “clinically isolated syndrome” (CIS). It is important for the diagnosis of CIS to exclude other neurologic diseases.
In case of CIS then it is of the outmost importance to know who will have other neurological symptoms and convert to a full condition of multiple sclerosis.
In the scientific literature, the risk from developing a clinically definite MS from CIS is estimated to be 42-82%.
It is not possible to define this risk only on the basis on the clinical features.
Some genetic factor (positivity for HLA-DRB1*1501) could increase this risk. The brain abnormalities which are visible with the MRI (number of T2 lesions, periventricular location, presence of gadolinium enhancing lesions, infratentorial lesions) and the presence of oligoclonal bands in the CSF are the most important predictors of conversion from CIS to clinically definite MS. Diffusion tensor imaging and MR imaging spectroscopy could give further elements.
The 2010 revised McDonald Criteria attempted to simplify the MS diagnostic criteria just in order to include under the diagnostic umbrella of MS as many as possible of patients with CIS (probably 15-20% of them).
There is some evidence that patient with CIS can benefit (reduction of the number of attacks, delayed progression to MS) from first-line immunomodulatory treatments that are introduced for multiple sclerosis. However, these treatments could have important side effects and one third of patients with CIS will not have other clinical relapses even without these treatments. Thus, treatment options for patients with CIS (after exclusion of other neurological diseases) should be always evaluated and accurately discussed with the single patient but this discussion is not always easy.
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