Examining the latent structure of negative symptoms: Is there a distinct subtype of negative symptom schizophrenia?

Abstract

Negative symptoms have emerged as a replicable factor of symptomatology within schizophrenia. Although rating scales provide assessments along dimensions of severity, categorization into a negative symptom subtype is typically conducted. A categorical view of negative symptoms is best reflected in the proposal that enduring, primary negative symptoms, or deficit symptoms, reflect a distinct subtype of schizophrenia [Carpenter, W.T., Heinrichs, D.W., Wagman, A.M.I., 1988. Deficit and nondeficit forms of schizophrenia: The concept. Am. J. Psychiatry 145, 578–583.]. Despite an accumulation of findings that support a categorical conceptualization, the data are also consistent with a dimensional-only model where negative symptom subtypologies simply reflect an extreme on a continuum of severity. Using taxometric statistical methods [Waller, N.G., Meehl, P.E., 1998. Multivariate Taxometric Procedures: Distinguishing Types From Continua. Sage, Newbury Park, CA.], the present study examined whether a taxonic, or latent class, model best describes negative symptoms in a sample of 238 schizophrenia patients. In order to obtain more stable estimates of symptoms, ratings on the Scale for the Assessment of Negative Symptoms [Andreasen, N.C., 1982. Negative symptoms in schizophrenia: Definition and reliability. Arch. Gen. Psychiatry 39, 784–788.] were averaged across two assessments over a 6-month period. Two taxometric methods, maximum covariance analysis (MAXCOV) and mean above minus below a cut (MAMBAC) identified a latent class or taxon with a base rate of approximately 28–36%. Members of the negative symptom taxon differed from the nontaxon class in that taxon members were more likely to be male and demonstrated poorer social functioning. Taxon and nontaxon schizophrenia patients did not differ in psychotic or affective symptoms. The findings converge to provide support for a categorical view of negative symptoms. Further research is required to replicate the present taxonic findings and to examine characteristics (including possible etiological factors) associated with this negative symptom taxon.