The featured paper is “Psychopathology in Verified Huntington’s Disease Gene Carriers” by Duijn and colleagues and freely available here. In the introduction the author states that the prevalence of psychiatric disorders in a Huntington’s disease lies somewhere between 33 and 76%. The authors undertake a literature search in order to further characterise the relationship between Huntington’s disease and psychiatric disorders.
The methodology section for the literatures search was exemplary. The author’s first of all clearly identify the databases they are using – Embase and PubMed but also specified each and every search term that was used. There are invariably search terms which have not been used but as psychiatric disorders cover such a broad domain it is difficult to see how search strategies can be comprehensive in practical terms. The authors have provided us with clarity in the methodology which allows for reproducibility. They also select only english language articles and exclude animal or psychophysiological studies and then go on to hand search the references sections of the articles they have retrieved for further relevant papers. Finally as they are looking to identify the cumulative prevalence with confidence intervals the authors apply strict inclusion criteria to the papers that they have retrieved. As they are applying such strict criteria to a field with a relatively small literature base inevitably they end up with only a handful of papers – seven to be precise. The majority of papers were excluded on the grounds that they didn’t provide information on the prevalence of psychopathology. Another 10% of the papers didn’t utilise standardised instruments for assessing psychopathology. The authors also note that the characteristics of many of the sample populations are not given and so they have assumed that all patients are outpatients.
Of these studies, six report the prevalence of depressed mood and the reported mean in several of the cases lies close to 40 per cent. They note that when DSM criteria were used the prevalence was 43%. With regards to anxiety they note that different rating instruments are associated with a large variation in prevalence rates. With irritability and within the results section the authors don’t mention the rating scales or psychometric measures that were used to measure the underlying construct. Again they identify a large variation in prevalence rates between studies. For apathy there is also a wide variation in reported prevalence rates of between 34% and 76%. With obsessive and compulsive symptoms the results were more interesting – roughly half of patients in one study had either obsessions or compulsion although this prevalence varied even more widely. Interestingly enough there were only two out of 27 people meeting DSM criteria for OCD. The prevalence of psychotic symptoms was 11% in one study and 0% was included in the confidence interval of several other studies.
In the discussion the authors draw conclusions from the results and elsewhere in the literature. What I found particularly interesting was their focus on relating motor symptoms to psychopathology. They make specific recommendations for future research, suggesting that the motor components of the UHDRS is used as a marker of underlying pathology. They speculate about a possible relationship between OCD and Huntington’s disease pathology given the involvement of the Striatum. Also very interesting is the suggestion that the previous association between Huntington’s disease and psychosis related to the late stage at which it it has previously been detected. They further suggest that this may have resulted in a previous misclassification as schizophrenia in some cases. This is a very interesting literature review using an excellent methodology with clearly presented results, a detailed discussion and clear recommendations.
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