Disability in patients with chronic neck pain: heart rate variability analysis and cluster analysis.

OBJECTIVES: Adequately addressing the scope of disability in patients with chronic neck pain is crucial in a clinical setting. The aim of this study was to determine the disease profile of patients with chronic neck pain and to analyze the factors related to the level of disability.
METHODS: We studied 121 patients with chronic neck pain. The following data were obtained from the participants: Chinese Health Questionnaire-12, the Pittsburgh Sleep Quality Index, the visual analog scale to pain, pressure pain threshold, the Neck Disability Index, and heart rate variability analysis. Cluster analysis was performed to divide patients into separate groups according to their presentations. A Pearson correlation was computed to analyze factors correlated with disability (Neck Disability Index). The significance level was set at P<0.05.
RESULTS: Cluster analysis yielded 3 groups of patients with distinct features. Group I had a sex composition similar to the original population, was younger, and displayed the lowest overall deficits. Group II included middle-to-older-aged women, and presented with a higher level of pain, psychological distress, sleep disorder, and disability. Group III, comprising middle-to-older-aged men, showed moderate symptom severity. Correlation revealed that the factors significantly associated with a high degree of disability were low heart rate variability, high pain intensity, older age, poor sleep quality, and high psychological distress. DISCUSSION: We suggest that 3 distinct subgroups of patients with chronic neck pain exhibit particular features. Furthermore, reduced heart rate variability was associated with subjective disability in these patients. Further study is advised to establish the pathologic mechanism and clinical applications of our findings.