Testing the hypothesis that formal thought disorders are severe mood disorders.

BACKGROUND

It was recently hypothesized by Lake (Schizophrenia Bulletin 2008; 34: 109-117) that Formal Thought Disorder (FTD) can be accounted for by a single disorder that is currently diagnosed as bipolar disorder.

OBJECTIVES

This study aimed to analyze the underlying dimensions of FTD and to examine to what extent FTD factors can be accounted for by clinical distractibility, attentional impairment, severity of mania, and familial liability of bipolar disorder and schizophrenia.

METHODS

Six hundred and sixty inpatients were assessed using a semistructured interview, and FTDs were assessed with the Thought, Language, and Communication scale. "Inattentiveness during Mental Status Testing" item of the Scale for the Assessment of Negative Symptoms scale and a composite mania score were used. The Family History-Research Diagnostic Criteria was used.

RESULTS

FTD is a multidimensional construct comprised at least 5 dimensions: disorganization, verbosity, poverty of speech, idiosyncratic thinking, and blocking. Clinical distractibility loadings split in 2 factors, disorganization and blocking, but it did not load on the mania-related (verbosity) factor. Attentional disturbance was significantly associated with each FTD factor except for idiosyncratic thinking, and these associations were largely independent from the severity of mania. The associations of FTDs with mania and attentional disturbances were independent from each other. FTD factors were not significantly associated with familial liability to bipolar or to schizophrenia.

CONCLUSIONS

Disorganization was the main FTD component. Distractibility was a core feature of FTD factors but it was not specifically accounted for by mania-related attentional impairment. The hypothesis of mutual interdependence between mania and attentional disturbance leading to FTDs could not be confirmed.