title: Heterogeneous sensory processing in persistent postherniotomy pain.
abstract: Previous studies on sensory function in persistent postherniotomy pain (PPP) have only identified pressure pain threshold to be significantly different from pain-free patients despite several patients reporting cutaneous pain and wind-up phenomena. However the limited number of patients studied hinders evaluation of potential subgroups for further investigation and/or treatment allocation. Thus we used a standardized QST protocol to evaluate sensory functions in PPP and pain-free control patients, to allow individual sensory characterization of pain patients from calculated Z-values. Seventy PPP patients with pain related impairment of everyday activities were compared with normative data from 40 pain-free postherniotomy patients operated>1 year previously. Z-values showed a large variation in sensory disturbances ranging from pronounced detection hypoesthesia (Z=6, cold) to pain hyperalgesia (Z=-8, pressure). Hyperalgesia for various modalities were found in 80% of patients, with pressure hyperalgesia in approximately 65%, and cutaneous (mechanical or thermal) hyperalgesia in approximately 35% of patients. The paradoxical combination of tactile hypoesthesia and hyperalgesia was seen in approximately 25% of patients. Increased pain from repetitive tactile and/or brush stimulation was found in 51%, suggesting a role of altered central nociceptive function in this subpopulation. A high incidence (26%) of pressure hyperalgesia was found in the contralateral groin, with a significant correlation (rho=0.58, p=0.002) to the hyperalgesic level on the painful side, again suggesting central nervous mechanisms in PPP. In conclusion, this study shows that a standardized trauma results in heterogeneous combinations of hypo- and hyperalgesia. Z-score evaluation of sensory function identifies subpopulations in PPP, which may be used in selecting surgical and/or pharmacological treatment strategies.
authors.affiliation: Section of Surgical Pathophysiology, Rigshospitalet, Copenhagen University, Denmark Danish Pain Research Center, Aarhus University Hospital, Aarhus, Denmark Department of Neurology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Eske Kvanner
authors.initials: EK
authors.lastname: Aasvang
authors.forename: Birgitte
authors.initials: B
authors.lastname: Brandsborg
authors.forename: Troels Staehelin
authors.initials: TS
authors.lastname: Jensen
authors.forename: Henrik
authors.initials: H
authors.lastname: Kehlet
mesh_terms: D000328:Adult; D006119:Groin / Q000503:physiopathology / Q000601:surgery; D006552:Hernia, Inguinal / Q000601:surgery*; D006801:Humans; D006930:Hyperalgesia / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology; D010149:Postoperative Pain / Q000175:diagnosis* / Q000503:physiopathology; D010812:Physical Stimulation; D018709:Statistics, Nonparametric
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