The official international definition of a relapse is a period in which a person with MS experiences an acute worsening of function that lasts for at least 24 hours, usually lasting for several days or weeks, followed by an improvement that lasts for at least one month.
'Acute worsening of function' can mean the development of completely new symptoms or previous symptoms coming back. Examples of this might be double vision or numbness and tingling in a leg without any other obvious cause. To be classed as a relapse, these new or recurrent symptoms must then wear off or improve over time. Once this improvement in symptoms has lasted for at least one month, it is known as 'recovery' or 'remission'. Sometimes there is a full recovery of all function following a relapse, but quite often a person is left with some residual problems.
Not everyone agrees with this definition but it is a reasonable guide to a relapse. However, sometimes people experience a short term worsening of symptoms lasting for a few minutes, hours or even days, which is not due to a relapse. An increase in body temperature due to an infection or following exercise can do this. If you are unsure whether you are having relapses, you might want to discuss this with your MS nurse or neurologist.
In considering whether someone is eligible for disease modifying drugs based on relapses, the guidelines
guidelines of the Association of British Neurologists say that the person's history of relapses should
be confirmed by neurological examination by a specialist or from another source (e.g., hospital or
General Practitioner's records, or through discussions with the patient's main caregiver), in addition
to the person's own experience.