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  • Updated 03.21.2023
  • Released 06.07.2010
  • Expires For CME 03.21.2026

Clinically isolated syndrome



A clinically isolated syndrome is a first symptomatic episode of central nervous system dysfunction due to inflammatory demyelination. Risk factors for conversion to clinically definite multiple sclerosis have been identified, and treatment of high-risk individuals may delay subsequent relapses. Individuals with a clinically isolated syndrome may demonstrate accelerated brain atrophy and mild cognitive impairments. Revisions to the diagnostic criteria for relapsing-remitting multiple sclerosis are associated with a reduction in time to diagnosis of clinically definite multiple sclerosis in some patients presenting with an initial inflammatory event. In this article, the author summarizes the diagnosis, evaluation, and prognostic implications of radiologically and clinically isolated syndromes.

Key points

• Clinically isolated syndromes such as optic neuritis, transverse myelitis, and other syndromes compatible with a first episode of CNS demyelination warrant prompt evaluation to determine underlying etiology.

• Clinically isolated syndrome evaluation may yield important prognostic information regarding risk of multiple sclerosis, or may reveal an alternative diagnosis.

• Early treatment of select clinically isolated syndrome patients may delay subsequent relapses and eventual conversion to clinically definite multiple sclerosis.

• A “radiologically isolated syndrome” may have similar clinical significance to clinically isolated syndromes.

Historical note and terminology

The first journal article including the term “clinically isolated syndrome” appeared in 1993 (37). Increasing availability of MRI technology in the 1980s improved diagnosis of CNS demyelinating disorders, and the arrival of FDA-approved disease-modifying medications for multiple sclerosis starting in 1993 increased the importance of correct diagnosis and treatment. Long-term follow-up studies of patients presenting with an isolated clinical syndrome characteristic of multiple sclerosis led to the identification of baseline risk factors for conversion to clinically definite multiple sclerosis. Subsequent studies of clinically isolated syndrome patients revealed that early treatment with disease-modifying drugs may be beneficial in delaying a second demyelinating attack (23; 08; 22; 33).

Other descriptions of clinically isolated syndromes include: clinical onset of multiple sclerosis, isolated demyelination syndrome, first demyelinating episode, first presentation of multiple sclerosis, first attack of multiple sclerosis, and focal isolated idiopathic inflammatory demyelinating disorders.

The term “radiologically isolated syndrome” has evolved to describe individuals with brain MRI lesions suggestive of demyelination but without any associated clinical symptoms (44).

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