Fibromyalgia and CNS Dysfunction

Research on fibromyalgia (FM) has recently focused on disturbances in the central nervous system (CNS). McDermid et al.¹ reported generalized hypervigilance in FM patients, and Wachter et al.² recently published a study that found evidence of overactivity of the sympathetic nervous system in patients with fibromyalgia and other pain syndromes.

A current study examined 168 fibromyalgia patients to determine if there indeed was evidence of CNS dysfunction. All patients underwent an auditory brainstem response test (ABR), used to test the function of the cochlear nerve and auditory pathway in the brainstem; an oculomotor test, which monitors the neurological systems responsible for eye motor function; and a electronystagmography test (ENG), which measures vestibular function.

Researchers found:

• 78% of the FM patients complained of dizziness or vertigo. Most of these cases were mild, but 4% complained of constant, severe dizziness.
• Sensorineural hearing loss was found in 15% of the FM patients.
• 51 of the subjects (30%) had abnormal ABR test findings.
• 58% of the FM subjects had abnormal eye movement tests, and 45% had abnormal findings on the ENG test.

Similar findings have been found in whiplash injuries (see Soft-Tissue Review, Volume 1, Nos. 4,9,10.) What has not been determined is the root cause of this disturbance. Some speculate that the vestibular dysfunction arises from injury to the brainstem; others believe that proprioceptive disturbance in the cervical spine is responsible.

The issue is complex. On one had, the authors report that the nature of the abnormal ABR tests "strongly indicate that dysfunction involving the pons is common in patients with fibromyalgia." Then, in another paragraph, they state, "The interpretation of the findings of abnormal saccades and smooth pursuits as well as abnormal ENG registrations is that of CNS dysfunction, most likely in the posterior fossa. However, disturbances of smooth pursuits and also, to some extent, of saccades, can be seen in patients with tension headache without neurological signs and symptoms. The explanation of this observation is that proprioceptive dysfunction in the neck might cause erroneous signals which could disturb the oculomotor regulation."

In short, fibromyalgia shows some similarities to whiplash. It is not know whether these objective findings are due to problems in the brainstem or to disturbance of neck proprioception. As more studies are conducted, hopefully we can discover the answer to this problem.

1. McDermid AJ, Rollman GB, McCain GA. Generalized hypervigilance in fibromyalgia: evidence of perceptual amplification. Pain 1996;66:133-144.
2. Wachter KC, Kaeser HE, Guhring H, et al. Muscle damping measured with a modified pendulum test with patients fibromyalgia, lumbago, and cervical syndrome. Spine 1996;21(18):2137-2142.
3. Rosenhall U, Johansson G, Orndahl G. Otoneurologic and audiologic findings in fibromyalgia. Scandinavian Journal of Rehabilitation Medicine 1996;28:225-232.