Diagnosing sensory abnormalities with either normal values or values from contralateral skin: comparison of two approaches in complex regional pain syndrome I.

BACKGROUND To diagnose sensory abnormalities, patient values can be compared with values of the general population (absolute approach) or to values measured at contralateral homologous skin (relative approach). The current study gives normal values for both approaches and compares the advantages of each method by applying the technique to patients with complex regional pain syndrome type I (CRPS I). METHODS In 50 healthy control subjects, sensory and pain thresholds were measured for pressure, warmth, and cold on both wrists and both feet. In 53 patients with unilateral CRPS I (33 hand, 20 foot), the same assessments were conducted twice, at an interval of 1 month. RESULTS In control subjects, contralateral homologous sides have approximately the same sensitivity, supporting the validity of the relative approach in patients. Hypoesthesia and allodynia can be diagnosed by either the absolute or relative approach, whereas hyperesthesia and hypoalgesia can only be identified with the relative approach. The two approaches obtain different results in 20% of cases. Age, gender, and subject criteria may influence the absolute but not the relative approach. Both approaches are comparable with regard to reproducibility. Frequency distributions of sensory abnormalities in chronic CRPS I are presented. The most frequent diagnoses were cold allodynia and mechanical hypoesthesia and allodynia. CONCLUSIONS To divide sensory characteristics into a binary classification of "normal" and "abnormal," the relative approach is the best choice, with the exception of cases in which the contralateral homologous side is absent or affected by disease. The authors recommend the relative approach for both research and clinical purposes.