Clinical problem

The clinical diagnosis of multiple sclerosis is made on the evidence of two or more lesions in the CNS and the exclusion of all other possible causes. Clinically, MS is characterized by exacerbation and remission of symptoms, and the disease’s diagnosis is classified into definite, probable, and possible.

ABR and MLR confirm lesions in the CNS in a high proportion of cases. These tests can also detect unsuspected lesions, which is their main value for the clinician in making the diagnosis. It should be noted that visual-evoked potentials (VEP) and somatosensory-evoked potentials (SEP) reveal silent lesions more frequently than does ABR. For many patients who present with symptoms indicating a single lesion, evoked-potential measurements can demonstrate subclinical abnormalities in areas other than the presenting symptom, and thereby clarify the diagnosis.

ERA tests and strategies

Patients with clinical evidence of brainstem lesion at the time of recording have a higher proportion of ABR and MLR abnormalities than do those who do not show brainstem disorders (see Chs. 7 and 9). Among the latter group, however, some investigators describe abnormal ABR in 20–50% of patients (Chiappa & Ropper 1982).

The particular diagnostic value of using evoked potentials, including ABR, is in detecting silent lesions in patients for whom the diagnosis is uncertain.

Rudge (1983) has suggested that it is worth recording MLR, in addition to ABR. In a group of patients with definite multiple sclerosis, many patients with abnormal ABR also have abnormal MLR, and in about 12% of patients with normal ABR, the MLR was abnormal. In the less than definite group of MS patients, the results are similar to those with a definite diagnosis of MS.

A useful clinical procedure is to test, and then raise the patient’s body temperature by 1°C, and retest. The increase in temperature causes further abnormalities in previously abnormal responses and can reveal previously silent lesions.

Bilateral recording of ABR should be done, as it can reveal lesions of the crossing pathways from an analysis of the contralateral response.