Pain Insensitivity and Pressure Pain Thresholds in Patients with Schizophrenia

Song, Ji Young; Yi, Jang Ho

Abstract

OBJECTIVES
Decreased pain sensitivity to the external stimuli was sought by measuring the pressure pain thresholds in patients with schizophrenia. In the case of the pain insensitivity(PI) being confirmed, the relationship between psychiatric symptoms and PI was to evaluated.
METHODS
21 schizophrenic and 23 healthy controls were enrolled. Pressure pain thresholds(PPT) were measured by pressure algometer on initial and recovered phase, and positive and negative symptoms by PANSS(Positive and Negative Symptoms Scale)(Stanley et al. 1991) were obtained in patient group. The confounding factor induced by antipsychotics to the PPT was controlled for. Comparisons of PPT between two groups, and correlations of PPT and psychiatric symptoms in patient group were tested.
RESULTS
1) Schizophrenic patients with active psychotic symptoms showed higher PPT compared to healthy controls. 2) When psychiatric symptoms were improved, PPT was decreased to the level of healthy controls. 3) Only the subscale of delusion in PANSS was closely correlated with PPT in patients with schizophrenia. 4) The dose of antipsychotics did not influence the PPT of the patient group.
CONCLUSIONS
A part of patients with schizophrenia revealed they had higher pressure pain thresholds, which suggested PI in active symptom phase. However, PPT were restored almost to the level of normal controls when psychotic symptoms were improved. Thus, PI seemed to be a transient phenomenon rather than a persistent one. Changes of pain sensitivity to the external stimuli in schizophrenics would be associated with severity of delusion based upon reversible changes of brain function. Decreased attention due to delusion or lack of motivation seemed to be causal factors of PI. Clinicians should give attention to PI in schizophrenic patients to prevent physical illness and serious injuries in them.