The P300 wave is an event related potential which is used to assess cognitive function, it is recorded as positive deflection in voltage at latency of roughly 300 ms. P300 latency suggests that shorter latency times are related to cognitive performance. This study was undertaken to evaluate objectively effect of hypothyroidism on latencies of ERPs and response to thyroxine replacement.
Biochemically proven new onset cases with hypothyroidism were enrolled into study. After detailed history and physical examination and routine biochemical investigations P300 cognitive potentials were recorded using a Nicolet Viking Select neuro-diagnostic system version 10.0. Study was done in electrophysiology lab in Osmania Medical College.
Results: Patient characteristics (i.e age, sex, BMI) of both cases and controls were comparable. Cases consisted of 2 groups overt hypothyroid cases −24, mean TSH values in them was 94.1.subclinical −21 cases in whom mean TSH value was 12.3.
Mean P300 latencies of all cases at Cz was 342.42±29.5, and at Pz was 345.4±30. Mean P300 latencies of controls at Cz was 296.4±34 and at Pz was 297.9±33.Difference between cases and controls was highly significant p value<0.001. Mean P300 values in overt cases was 362.6±32.9 at Cz, and at Pz it was 362.5±33.9. Mean P300 values in subclinical cases was 319.3+/30.9at Cz, and at Pz it was 316.4±27.9. P300 values in overt cases was highly significant compared to controls. Whereas p300 values in subclinical cases vs controls was just significant.
There was statistically significant difference in p300 values (at Cz and Pz) before and after treatment in overt (P value<0.001)as well as subclinical cases (P value<0.009).
P300 latency prolongation in both clinical and subclinical hypothyroid cases shows that cognitive function is affected adversely even in subclinical hypothyroid cases. Most psychometric tests assessing cognitive function can identify gross defects in cognition,hence these will not be able to detect subtle changes in subclinical hypothyroidism. Such subtle defects may not be of importance in elderly individuals but willaffect performance of younger individuals in day to day life.
This test of auditory evoked potentials p300 may be useful to identify patients with subclinical hypothyroidism who will benefit with treatment as against those who can be followed up.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.