Is psychomotor retardation a sixth domain of negative symptoms?

The five canonical domains of negative symptoms in schizophrenia - blunted affect, alogia, asociality, anhedonia, and avolition - were established by a consensus process. Meta-analyses have placed psychomotor retardation (PMR) rating scale items in negative symptom factors, suggesting it may be a sixth negative symptom domain.

We pooled data from two cross-sectional, multicenter, international studies of schizophrenia (N = 271) and used PANSS item G7 (Motor Retardation) as a measure of PMR. In multivariate analyses we examined G7 as a predictor of cognitive function, personal and social function, and negative symptoms other than PMR. We also examined whether G7 mediated the association between extrapyramidal symptoms and negative symptoms.

In some analyses the G7 factor had relationships characteristic of the five canonical domains: correlations with those negative symptoms and negative correlations with function and cognition. However, other findings were consistent with its classification as a motor symptom: significant correlations with the PANSS Mannerism and Posturing item and with extrapyramidal symptoms, and mediation of the relationship between extrapyramidal symptoms and the canonical negative symptoms. There was no significant relationship with self-reported hours of sleep.

PMR showed associations with negative symptoms, cognitive impairment, and functional outcome, consistent with status as a sixth negative symptom domain. However, other findings leave unclear whether it should be considered a negative symptom, a motor symptom, or something more complex. Problems in the G7 item definition and description contribute to this uncertainty.