Rapid detection of generalized anxiety disorder and major depression in epilepsy: Validation of the GAD-7 as a complementary tool to the NDDI-E in a French sample

Abstract

Objective: Generalized anxiety disorder (GAD) in people with epilepsy (PWE) is underdiagnosed and undertreated. The GAD-7 is a screening questionnaire to detect GAD. However, the usefulness of the GAD-7 as a screening tool in PWE remains to be validated. Thus, we aimed to: (1) validate the GAD-7 in French PWE and (2) assess its complementarity with regard to the previously validated screening tool for depression, the Neurological Disorders Depression Inventory for Epilepsy (NDDI-E).

Methods: This study was performed under the auspices of the ILAE Commission on Neuropsychiatry. People with epilepsy >18 years of age were recruited from the specialist epilepsy unit in Marseille, France. The Mini-International Neuropsychiatric Interview (MINI) was performed as gold standard, and the Penn State Worry Questionnaire (PSWQ) and the NDDI-E were performed for external validity. Data were compared between PWE with/without GAD using Chi(2) test and Student's t-test. Internal structural validity, external validity, and receiver operator characteristics were analyzed. A principal component factor analysis with Varimax rotation was performed on the 13 items of the GAD-7 (7 items) plus the NDDI-E (6 items).

Results: Testing was performed on 145 PWE: mean age = 39.38 years old (SD=14.01, range: 18-75); 63.4% (92) women; 75.9% with focal epilepsy. Using the MINI, 49 (33.8%) patients had current GAD. Cronbach's alpha coefficient was 0.898, indicating satisfactory internal consistency. Correlation between GAD-7 and the PSQW scores was high (r (145)=.549, P<.0001), indicating good external validity. Factor analysis shows that the anxiety investigated with the GAD-7 and depression investigated with the NDDI-E reflect distinct factors. Receiver operator characteristic analysis showed area under the curve of 0.899 (95% CI 0.838-0.943, P < 0.0001) indicating good capacity of the GAD-7 to detect GAD (defined by MINI). Cutoff for maximal sensitivity and specificity was 7. Mean GAD-7 score in PWE with GAD was 13.22 (SD = 3.99), and that without GAD was 5.17 (SD = 4.66).

Significance: This study validates the French language version of the GAD-7 screening tool for generalized anxiety in PWE, with a cutoff score of 7/21 for GAD, and also confirms that the GAD-7 is a short and easily administered test. Factor analysis shows that the GAD-7 (screening for generalized anxiety disorder) and the NDDI-E (screening for major depression) provide complementary information. The routine use of both GAD-7 and NDDI-E should be considered in clinical evaluation of patients with epilepsy.

Keywords: Epilepsy; Generalized anxiety disorder; Psychiatric comorbidity; Reliability; Screening tool; Validity.