Only cervical vertebrae C0-C2, not C3 are relevant for subgrouping migraine patients according to manual palpation and pain provocation: secondary analysis of a cohort study

BACKGROUND: Subgrouping of migraine patients according to the pain response to manual palpation of the upper cervical spine has been recently described. Based on the neuroanatomy and the convergence of spinal and trigeminal nerves in the trigeminocervical complex, the cervical segments C1 to C3 are potentially relevant. To date it has not been investigated whether palpation results of all upper cervical segments are based on one underlying construct which allows combining the results of several tests. Therefore, the aim of this secondary analysis of a cohort study was to determine whether results from all three segments form one construct. METHODS: Seventy-one migraine patients with chronic or frequent episodic migraine diagnosed according to the international headache society classification version 3 were examined by one physiotherapist. Manual palpation using a posterior to anterior pressure was performed on the upper three cervical vertebrae unilaterally left and right. The results of the palpation according to the patients’ responses were combined using factor analysis. In addition, item response theory (IRT) was used to investigate the structure of the response pattern as well as item difficulty and discrimination. FINDINGS: Factor analysis (principal component) showed that the palpation of C3 loads less onto the underlying construct than the palpation of C1 and C2. Considering a cut-off value > 1.0, the eigenvalues of all three segments do not represent one underlying construct. When excluding the results from C3, remaining items form one construct. The internal consistency of the pain response to palpation of C1 and C2 is acceptable with a Cronbach’s alpha of 0.69. IRT analysis showed that the rating scale model fits best to the pain response pattern. The discrimination value (1.24) was equal for all items. Item difficulty showed a clear hierarchical structure between the palpation of C1 and C2, indicating that people with a higher impairment are more likely to respond with referred pain during palpation of C2. CONCLUSION: Statistical analysis confirms that results from the palpation of the cervical segments C1 and C2 in migraine patients can be combined. IRT analysis confirmed the ordinal pattern of the pain response and showed the higher probability of a pain response during palpation of C2. The pain response to C3 palpation is not relevant for unidimensional IRT analysis. TRIAL REGISTRATION: German registry of clinical trials (DRKS00015995), Registered 20. December 2018, https://www.drks.de/drks_web/setLocale_EN.do