Complex regional pain syndrome and migraine: Clinical relationships and possible common aetiology

BackgroundMigraine headache and complex regional pain syndrome share mechanisms, such as neuroinflammation, central sensitization and loss of inhibitory pain controls, that could provoke or exacerbate symptoms in both disorders. In the present study, it was hypothesized that headaches would worsen after the onset of complex regional pain syndrome and that limb pain would be more severe in patients with co-morbid headaches than in patients who remained headache-free. Notably, complex regional pain syndrome is associated with ipsilateral cranial symptoms such as photophobia and forehead hyperalgesia. Whether shared mechanisms might drive these symptoms was also explored.MethodsEighty-eight patients with complex regional pain syndrome were asked about their previous and current headache experience. The spatial distribution of pain was quantified from pain drawings, and hyperalgesia to mechanical and thermal stimulation was assessed in the limbs and forehead. In addition, the visual discomfort threshold was measured separately for each eye.ResultsSixty-six percent of patients reported that headaches (primarily migraine) had developed or worsened after the onset of complex regional pain syndrome and 22 percent now had daily or near-daily headaches. Limb pain and hyperalgesia were greater in such cases than in those with stable headaches or who remained headache-free. Photophobia and forehead hyperalgesia were greater ipsilateral than contralateral to symptoms of complex regional pain syndrome in patients with stable or worsening headaches but were symmetrical in headache-free patients. In addition, photophobia was symmetrical in patients with recurrent tension-type headaches. Patients with worsening headaches were younger at the onset of complex regional pain syndrome than patients with stable headaches or who were headache-free, in line with greater vulnerability to migraine in younger than older adults. In a subgroup of patients, the pain of complex regional pain syndrome extended from the upper limb to the ipsilateral dorsal cervical region, a documented source of pain in migraine. However, headaches ipsilateral to complex regional pain syndrome also recurred in patients with lower limb pain, indicating involvement of other pain mechanisms.ConclusionsTogether, the findings indicate that headaches with features of migraine develop after the onset of complex regional pain syndrome. In turn, this is associated with ipsilateral cranial symptoms and heightened limb pain. We suggest that shared pathophysiology increases susceptibility to ipsilateral cranial symptoms and exacerbates pain in both disorders, potentially in a positive loop. Breaking this cycle might permit otherwise intractable symptoms and pain to subside.