Does spinal manipulation do any good for chronic headache?

Is there any evidence that chiropractic adjustments help chronic headache? A study just published in The Spine Journal begins with the observation:

"Systematic reviews of randomized controlled trials suggest that spinal manipulative therapy (SMT) is efficacious for care of cervicogenic headache (CGH). The effect of SMT dose on outcomes has not been studied."

Eighty patients with chronic cervicogenic (originating in the neck) headache were randomised for treatment with either spinal manipulation or massage therapy and their outcomes analyzed. What did the data show?

"There was an advantage for SMT over the control...For the higher dose patients, the advantage was greater. Patients receiving SMT were also more likely to achieve a 50% improvement in pain scale...Secondary outcomes showed similar trends favoring SMT. For SMT patients, the mean number of CGH was reduced by half."

The conclusion:

"Clinically important differences between SMT and a control intervention were observed favoring SMT."

In light of the importance of the role of cytokines such as TNF-α (tumor necrosis factor-alpha) in chronic inflammation, a case review recently published in the Journal of Manipulative and Physiological Therapeutics that documents a marked improvement associated with recovery from cervicogenic headache has a result of SMT:

"Two patients with whiplash injury and disk herniation developed CHA (cervical headache) associated with very high TNF-α levels. After manipulative therapy, these patients became symptom-free, and their TNF-α levels decreased substantially."

The study size is only two patients, but it's consistent with the findings of another study published in the same journal that show the connection between recovery from headache by manual therapy and improvements in Heart Rate Variability (analysis of changes in the intervals between heartbeats that reveals autonomic nervous system function) and mood:

"The purpose of this study was to investigate the immediate effects of head-neck massage on heart rate variability (HRV), mood states, and pressure pain thresholds (PPTs) in patients with chronic tension-type headache (CTTH)."

Heart Rate Variability is a powerful indicator of the functional state of the part of the nervous system that automatically "runs" the internal organs and functions. Most chronic conditions are characterized by excessive activity of the sympathetic nervous system (SNS) and deficient parasympathetic nervous system (PSNS) resources and less overall variability (more rigidity). The author's data led to this conclusion:

"The application of a single session of manual therapy program produces an immediate increase of index HRV and a decrease in tension, anger status, and perceived pain in patients with CTTH."

This is impressive, and duplicates my own clinical experience with treatment and HRV analysis. These findings help establish the scientific basis for why people feel so much better after their treatments.