Introduction Compared to migraine and tension headache, headaches of cervical origin are better understood in terms of anatomy and physiology yet are least well accepted. What is controversial is not whether cervical headaches occur, but how often they occur and how they can be reliably distinguished from other entities. Using controlled diagnostic blocks Lord ( Lord SM et al. J Neuro Neurosurg Psychiatry 1994, Barnsley L et al. Pain 1993) implicated the C2/3 zygapophysial (Z) joint as the primary source of referred pain in 58% of patients in whom headache was the dominant symptom following whiplash injury. There are no other equivalent studies. The purpose of the study was to determine the prevalence of cervicogenic headaches arising from the Z-joints; to determine their segmental origin, and to construct an evidence-based diagnostic and therapeutic algorithm.
Method Of 241 patients referred to a tertiary pain unit, with a history of posttraumatic chronic neck pain, 133 had accompanying headache which at times was a dominant feature. All 133 consented to undergo comparative diagnostic blocks under double blind conditions and each was randomly assigned to receive either lignocaine or bupivacaine (2) An independent observer recorded pre-and post-injection pain scores for the first 24 hours and where indicated, the alternative agent was injected a week later. A block was deemed to be successful when the patient reported total abolition of the index pain (i.e. VAS=0) on two separate occasions at least a week apart . The lateral atlantoaxial (C1/2) joints were blocked by intra-articular injection. Medial branch blocks were performed for the remaining synovial joints. The atlanto-occipital (C0/C1) joints were not accessed. All blocks were executed under aseptic conditions and with fluoroscopic guidance.
Results Of 191 joints investigated, 122 (64%) were positive. The C2/3 joint contributed 36% whilst the C3/4 and C1/2 accounted for 13% and 6% respectively. The C6/7 was implicated in one instance and the remaining 8% was equally shared between the C4/5 and C5/6 levels. Segmentally, the respective positive rates at C2/3 and C1/2 were 72% and 56%. Investigating the C1/2 joint was a later development and hence it is likely that the 6% is an underestimate and a proportion may remain “hidden” in the 28% C2/3 negatives. The upper three joints accounted for 85% of all positive blocks (N=122) and this correlates with the known neuroanatomy. In patients where headache was the dominant symptom, all 68 positive blocks (100%) were obtained at the upper three joints.
Discussion Cervicogenic headache is not uncommon and unlike other primary headaches can be diagnosed with certainty. The definitive criterion is complete relief of pain after controlled diagnostic blocks. Valid treatment is available (Govind J et al. J Neurol Neurosurg Psychiatry 2003). Early diagnosis and prompt treatment have considerable economic, non-economic and psychological benefits; with concomitant reduction in iatrogenesis, morbidity and mortality.
