Epidemiology and assessment of psychiatric disorders in epilepsy
This thesis addresses two important research questions. First, are common mental disorders commoner in epilepsy? Second, what are the instruments of psychiatric research that may be employed to assess psychiatric disorders in epilepsy? Two studies were conducted as part of this thesis: the first a primary care-based case-control study, and second, a study among institutionalised patients with epilepsy. Both studies used several psychiatric measures, and compared them with two gold standards: ICD-10 Criteria and "clinical significance" ratings. Common mental disorders were significantly commoner in the epilepsy group than among controls. The instruments tested demonstrated good sensitivity and specificity, and we present revised cut-off scores for epilepsy populations. Psychiatric symptoms specific to epilepsy were good predictors of psychiatric caseness. The psychiatric measures used appeared to correlate better with clinical significance ratings than with ICD-10 criteria. Psychiatric co-morbidity rather than seizure severity had a significant impact on subjective handicap. The institutional study revealed high rates of psychiatric co-morbidity, significantly more in patients with cognitive impairment. While different measures were correlated for overall psychiatric caseness, individual symptom categories were poorly correlated. An exploratory factor analysis of the NPI yielded a reliable and interpretable four-factor solution indicating good content validity. However, no measure appeared to perform well, against either "clinical significance or ICD-10 ratings, indicating poor concurrent validity. These studies show that psychiatric co-morbidity is over-represented in epilepsy, and that it has a significant impact on disablement. Symptom-based measures of psychological burden may be more sensitive than conventional criteria in identifying psychiatric disorders in epilepsy. Both these studies favour the "clinical significance" approach in assessing patients with epilepsy. The burden of epilepsy specific psychiatric co-morbidity must also be explored systematically in future studies. The results from these studies underline the need for public health planners to address mental health issues in epilepsy.