Psychopathy and Sadism: A Systematic Review of Their Association, Core Dimensions, and Nosological Implications

This systematic review aimed to synthesize the available scientific evidence on the relationship between psychopathy and sadism. It was conducted in accordance with the PRISMA 2020 guidelines and prospectively registered in the International Prospective Register of Systematic Reviews (PROSPERO, CRD420261394636). Included studies had to assess both constructs using validated instruments such as the Psychopathy Checklist-Revised (PCL-R), the Self-Report Psychopathy Scale (SRP), the Levenson Self-Report Psychopathy Scale (LSRP), the Psychopathic Personality Inventory-Revised (PPI-R), or the Triarchic Psychopathy Measure (TriPM) for psychopathy and clinical or behavioral scales for sadism or sexual sadism. A literature search was performed in PubMed/MEDLINE, Scopus, and Web of Science using terms related to psychopathy, sexual violence, sexual aggression, and sadism, combined with Boolean operators. Two reviewers independently performed study selection and data extraction, while methodological quality was assessed using the Newcastle-Ottawa Scale (NOS), Cochrane Risk of Bias version 2 (RoB 2), and AMSTAR-2 (A Measurement Tool to Assess Systematic Reviews 2) tools. The certainty of the evidence was evaluated using the GRADE framework. According to the PRISMA flowchart, 1,061 records were identified. After removing 239 duplicates and applying the selection criteria, 18 studies (19 reports) involving 12,302 participants with a mean age of 34.01 ± 9.98 years were included. The evidence consisted of 16 observational studies and two meta-analyses. The studies primarily focused on forensic, clinical, and prison populations, and there was a predominant representation from Europe and the Americas (42.11% each). The studies used validated instruments, such as the PCL-R, LSRP, SRP, and TriPM, as well as specific scales for sexual and everyday sadism. Meta-analyses identified moderate to significant positive correlations between global psychopathy and sadism (r = 0.24, 95% CI: 0.16-0.34, p < 0.001) and between psychopathy and sexual sadism (r = 0.33, 95% CI: 0.21-0.44, p < 0.001). However, there was high heterogeneity (I² = 84.5-92.3%). Individual studies revealed positive correlations between psychopathy and sadism ranging from low to moderate (r = 0.16-0.53). However, some studies found no significant associations. Individuals with sadistic characteristics generally had higher psychopathy scores than non-sadistic subjects. Significant differences in PCL-R scores were observed between sadistic and non-sadistic groups (21.49 vs. 17.12; p = 0.004; d = 0.59) and between sexual offenders with and without sadism (27.0 vs. 19.0; p = 0.01). Nevertheless, some findings were contradictory, with studies failing to identify a specific relationship between psychopathy and sexual sadism. Analysis of the psychopathic dimensions revealed that the antisocial, impulsive, and affective components exhibited the strongest associations with sadism. The antisocial facet predicted sexual aggression (r = 0.48, β = 0.26, p < 0.001), and the affective dimension showed significant associations with sexual sadism (β = 0.27). In dimensional models, "malice" and disinhibition were the components most strongly related to sadism, while audacity showed weak associations. Among a non-forensic population, latent correlations between psychopathy and everyday sadism were very high (ρ = 0.94-0.98), suggesting a possible conceptual overlap between the two constructs.