Phenotypic Variation in Complex Regional Pain Syndrome: Comparison Between Presentation in Knee Alone or in Ankle/Foot.

Objective: To compare the phenotypes of patients with complex regional pain syndrome (CRPS) of the knee to those with CRPS of the ankle/foot.

Setting: A retrospective study.

Subjects: Patients with CRPS of the knee and patients with CRPS of the ankle/foot.

Methods: We used electronic patient databases to identify patients with CRPS of the knee and patients with CRPS of the ankle/foot. The following variables were recorded: age, gender, duration of complaints, initial injury, and symptoms and signs. Frequency distributions and statistical significant differences between the groups were determined.

Results: Included were 50 patients with CRPS of the knee and 64 patients with CRPS of the ankle/foot. These patients were all diagnosed with CRPS according to the criteria used at the time of diagnosis. No significant differences were found in demographic characteristics. A few symptoms and signs appeared to be proportionally more prevalent in patients with CRPS of the ankle/foot. However, patients with CRPS of the knee suffered significantly longer from the disease than patients with CRPS of the ankle/foot.

Conclusions: Some signs and symptoms appeared to be statistically significantly more prevalent in CRPS of the ankle/foot than in CRPS confined to the knee. We conclude that the phenotypes of CRPS confined to the knee and CRPS of the ankle/foot are comparable, but not identical. This can be a reason why CRPS in patients with pain of the knee, that is disproportionate to the initial trauma, is sometimes not recognized.