Pain modulatory phenotypes differentiate chronic pancreatitis patients with distinct clinical pain profiles

Larsen IM, Faghih M, Phillips AE, Drewes AM, Singh VK, Yadav D, Olesen SS

Background and aims: Pain therapy remains challenging in chronic pancreatitis (CP) patients. Methods based on quantitative sensory testing (QST) provide information on pain modulation. This study explores the existence of CP subgroups with different pain modulatory phenotypes and investigates associations with patients’ clinical pain and psychological profiles. 
Methods: This was a cross-sectional, multicentre study. Patients completed questionnaires and a standardized QST protocol was used to record pain detection thresholds (PDTs) to muscle pressure stimulations at pancreatic dermatomes and three control areas. Ratio between pancreatic and control PDTs were calculated (PDT-index) to offset inter-individual differences.
PDT-index was used with repetitive pinprick stimulations, applied at the abdominal pancreatic dermatome, to obtain a measure of segmental hyperalgesia. Conditioned pain modulation (CPM) paradigm was performed to investigate descending pain modulation. Patients were grouped based on normative QST reference values and questionnaire scores were compared across subgroups to investigate associations with clinical pain and psychological profiles.
Results: Ninety-one patients completed the study. Four distinct pain modulatory phenotypes were found: group 1 (n=34) had normal pain modulation; group 2 (n=27) had impaired CPM; group 3 (n=14) had segmental hyperalgesia; and group 4 (n=16) had impaired CPM and segmental hyperalgesia. Significant differences in pain scores were observed across subgroups (all p<0.05). Psychological profiles were comparable across subgroups.
Conclusion: Patients with segmental hyperalgesia and impaired CPM have significantly more pain compared to their counterparts. As psychological profiles were not dependent on pain modulatory phenotypes, QST provides an unbiased mean for characterization of pain on an individual patient level.

PAIN MODULATORY PHENOTYPES DIFFERENTIATE CHRONIC PANCREATITIS PATIENTS WITH DISTINCT CLINICAL PAIN PROFILES