Quantitative testing of pain perception in subjects with PTSD - Implications for the mechanism of the coexistence between PTSD and chronic pain

Post-traumatic stress disorder (PTSD) often co-occurs with chronic pain. Neither the underlying mechanism of this comorbidity nor the nature of pain perception among subjects with PTSD is well defined. This study is the first systematic and quantitative evaluation of pain perception and chronic pain in subjects with PTSD. The study group consisted of 32 outpatients with combat- and terror-related PTSD, 29 outpatients with anxiety disorder and 20 healthy controls. Quantitative somatosensory testing included the measurement of warm, cold, light touch and heat-pain thresholds and responses to acute suprathreshold heat and mechanical stimuli. Chronic pain was characterized, and levels of PTSD and anxiety symptomatology were assessed by self-report questionnaires. Subjects with PTSD exhibited higher rates of chronic pain, more intense chronic pain and more painful body regions compared with the other two groups. PTSD severity correlated with chronic pain severity. Thresholds of subjects with PTSD were significantly higher than those of subjects with anxiety and healthy controls, but they perceived suprathreshold stimuli as being much more intense than the other two groups. These results suggest that subjects with PTSD exhibit an intense and widespread chronic pain and a unique sensory profile of hyposensitivity to pain accompanied by hyper-reactivity to suprathreshold noxious stimuli. These features may be attributed to the manner with which PTSD subjects emotionally interpret and respond to painful stimuli. Alternatively, but not mutually exclusive, the findings may reflect altered sensory processing among these subjects.