Diagnosis of Multiple Sclerosis

The diagnosis is clinical, and there is no single test that, on its own, can establish the diagnosis of multiple sclerosis. For this reason, a set of criteria (known as the McDonald criteria) is used, which includes:

• Clinical manifestations indicative of a demyelination lesion.
• Presence of lesions in magnetic resonance (MR) scan, which must meet a series of established characteristics.
• Exclusion of other situations that could produce a similar clinical picture.

Taken together, the criteria help to define that there are two different areas of the central nervous system (CNS) involved and at two distinct times. That is to say, there is involvement in different areas of the CNS (dissemination in space) and at different times during the course of the disease (dissemination in time), which is what characterises the disease.

The criteria are established in order to diagnose those patients who have symptoms suggestive of demyelination, and, thus, in those in whom the disease is suspected, and not to differentiate the disease from other neurological disorders.

Therefore, the diagnosis requires:

• A targeted clinical history (anamnesis) to determine whether the patient's symptoms are consistent with the disease.
• A neurological examination, which allows the detection of abnormalities affecting these areas.
• Evaluation and interpretation of the magnetic resonance imaging (MRI) findings in the context of the individual patient. This is important because the lesions seen on MRI are not specific; however, depending on their location, size, and distribution, they may be highly suggestive of multiple sclerosis. MRI is therefore useful for demonstrating the presence of multiple lesions, indicating dissemination in space, and for ruling out other diseases and conditions.

It is important that a neurologist—if possible  familiar with the disease—applies the criteria and makes the multiple sclerosis diagnosis.