Greater occipital nerve blockade for the treatment of chronic migraine

Dear Editor,

We would like to thank Dr. Solomon (1) for their interest (2). First, the local anaesthetic sensitivity of nerve fibres varies widely among individual patients. The pain sensation cannot be eliminated at each application. The frequency and voltage dependent effects of local anaesthetics can be affected by many factors (e.g. the pK_a value, molecular size and solubility in fat tissue) (3).

In our daily practice, we have observed that, after the blockade of the greater occipital nerve, some patients do not experienced numbness. Stopping the transmission of pain and sensation may not be recognized, thus detailed sensory examinations such as the pinprick test may be needed to show hypoesthesia and analgesia in the area of the greater occipital nerve. Some patients reported that they only felt a local pressure. Infiltration of saline around the area of the greater occipital nerve may have volume and pressure effects and may cause sensations of tingling and numbness, which may also simulate a local anaesthetic effect. Based on these observations, patients were told beforehand that there may or may not be numbness, and that this depended on the perception of the patients.

Second, there may be anatomic variations between patients and, as we used anatomic landmarks, it was not possible to pinpoint the exact nerve location (4). Even though some patients in the bupivacaine group were not blocked as might be expected, the results for the bupivacaine group were superior to those in the placebo group.