Self-harm leads to heightened tolerance to pain in BPD patients
MedWire News: Patients with borderline personality disorder (BPD) have a blunted sensation of pain caused by repeated self-inflicted injury, shows research.
Non-suicidal self-injurious behaviour (SIB) occurs in 70 to 80% of patients with BPD, say study authors Walter Magerl et al (Ruprecht Karls-University Heidelberg, Germany).
"Importantly, the majority of BPD patients with SIB claim that their self-injury is not painful," they explain. "Likewise, BPD patients also display a relative insensitivity to experimental pain, namely to cold and heat pain."
In this study, published in the journal Pain, the team investigated pain sensitivity in the participants by probing two unrelated nociceptive pathways by pinprick and capsaicin injection. They also examined and whether the results obtained were linked to BPD severity or recency of SIB.
The study included 15 women and seven men with BPD with an average age of 29 years, who were compared against 22 age- and gender-matched controls.
The patients with BPD showed significantly lower pain ratings compared with the controls: 28% lower in the patients with BPD compared with the controls when tested with pin prick and 38% lower when tested with capsaicin stimulation. The capsaicin-induced pain also decayed significantly faster in the patients with BPD compared with the controls.
The differences in sensitivity to pain between the patients with BPD and the controls were generally found in the female participants and not in the men.
The researchers found that recency of SIB was significantly correlated with the blunting of pain sensation in the BPD patients. The patients whose last self-injury was over a year before the examination had a "normal" pricking pain threshold of 43 mN, patients whose last self-injury was approximately 1 month ago had a threshold of 145 mN, and those whose average time since last injury was 1.5 days had a threshold of 326 mN.
The majority of the patients with BPD (n=19) were taking one drug or more at the time of the investigation, including selective serotonin reuptake inhibitors and/or noradrenalin, in some cases in combination with tricyclic antidepressants. However, no difference was found in pain rating between patients taking different drug groups or between patients who were not taking any medication and those that were.
From the reduced pain sensitivity with BPD compared with controls involving two distinct nociceptive sensory channels, the researchers induce that this reduction is "generalized and independent of nociceptive modality."
They conclude: "Correlation of hypoalgesia with recency of SIB, but not psychometric scales, suggests that hypoalgesia may result from a learning process caused by self-injury. Thus, BPD may be a model disease pinpointing the capacity of plasticity in endogenous pain control."
By Chloe McIvor