The Problem Of Depression Diagnosis In Epilepsy

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To conclude, a definite diagnosis of depression in patients with epilepsy can be difficult because a number of symptoms, which are recognized as diagnostic criteria for a depressive episode by the ICD-10 and DSM-IV, may occur in epilepsy secondary to seizure activity or AED treatment (e.g., loss of energy, insomnia or hypersomnia, increase or decrease in appetite, loss of libido, psychomotor agitation or retardation, diminished ability to think or concentrate). Because these symptoms may be present in patients who are not depressed, physicians need to explore fully the mental status of their patients. Inquiring about anhedonia has been suggested as an excellent predictor of the presence of depression (Kanner, 2006) and the use of self-rating instruments can be revealing. However, one of the most frequent methodological errors in research studies on depression and epilepsy is the sole reliance on screening instruments to diagnose depressive disorders. Firstly, a depressive episode can occur as part of a major depressive disorder, a bipolar disorder or as part of a double depression, which consists of recurrent major depressive episodes during a dysthymic disorder. Secondly, it is established that up to 50% of mood disorders identified in patients with epilepsy present with atypical clinical characteristics that fail to meet any of the DSM Axis I categories (see above) (Kanner, 2006).

In a recent paper, Krishnamoorthy (2006) reviewed instruments available for the evaluation of behavioral disturbances in epilepsy, pointing out that the vast majority of studies use measures or cut-off scores that may not be valid in the epilepsy population. At present, no measures exist that have been developed de novo for the assessment of comorbid psychopathology in epilepsy, using modern techniques of questionnaire development.

Krishnamoorthy (2005) suggested an adapted version of the SCID-I, named SCID-E. Mintzer and Lopez (2002) proposed the Epilepsy Addendum for Psychiatric Assessment (EAPA), an instrument expressly designed for use with the MINI. However, the relative benefits of these various instruments, in the assessment of generic psychopathology in community-based studies, are the subject of considerable debate. The psychometric properties of the Beck Depression Inventory (BDI), a well-known self-rating scale, to detect the severity of current (past 2 weeks) depressive symptoms, have been investigated in the epilepsy setting against the SCID-I, showing a good sensitivity (0.93), an acceptable specificity (0.81) and an excellent negative predictive value (0.98) but a very low positive predictive value (0.47) (Jones et al., 2005b). A six-item screening instrument, the Neurological Disorders Depression Inventory for Epilepsy (NDDI-E), was recently validated to screen for major depressive episodes in epilepsy (Gilliam et al., 2006). It has the advantage of being constructed specifically to minimize confounding factors, such as adverse events related to AEDs or cognitive problems associated with epilepsy, and showed an internal consistency of 0.85 and a test-retest reliability of 0.78. A score of 15 or higher has a specificity of 0.90 and a sensitivity of 0.81 for a diagnosis of major depression.

All the instruments discussed so far relate to a diagnosis of a mood disorder characterized by symptoms identical to those of the general population. However, it seems established that affective disorders in many patients with epilepsy are, in fact, different from those of non-epileptic patients and, in some cases such as the IDD, unique. The Seizure Questionnaire (Blumer et al., 2002) contains an inquiry for the eight key symptoms of the IDD. Patient and next of kin answer them jointly, and the examiner for completeness and accuracy then reviews all answers.

We have recently developed a specific questionnaire, named Interictal Dysphoric Disorder Inventory (IDDI) (see page 63). This is a 38-item self-report questionnaire where the eight key symptoms are evaluated in the first 32 items in terms of presence, frequency, severity and global impairment. The time-interval explored is the last 12 months. The six questions of the Appendix concern the time course of the disorder and relations of symptoms with seizures and therapy. As suggested by Blumer et al. (2004), a definite diagnosis of IDD is defined by the presence of at least three symptoms of at least "moderate" or "severe" severity that cause "moderate" or "severe" distress. Apart from the diagnosis, it is possible to obtain total and separate scores for key symptoms and the "severeness" of key symptoms, defined by severity, frequency and impairment scores (see page 66). The IDDI represents the first instrument for standardized diagnosis of IDD and its severity. It has been developed from a preliminary version of Krishnamoorthy and Trimble, and studies of validation against DSM-IV criteria for affective disorders are ongoing.

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