Background/Purpose: Fibromyalgia may be associated with central pain processing abnormalities, including central sensitization. In this study, we describe three patients, two females (41 and 48 years old) and one male (49 years old) who had no evidence of peripheral neuropathy on detailed electrophysiological studies. Each individual patient described a different sensory perception to the same controlled stimulus, suggesting abnormalities of central processing mechanisms. 

Methods: Detailed electrophysiological studies including motor sensory nerve conduction as well as late response studies were performed using a TECA EMG machine. Patients were asked to report the sensation they felt when electrical stimulation was delivered to peripheral nerves. The stimulus consisted of single electrical pulses of 0.1to 0.5 msec. duration. The stimulus intensity was adjusted to deliver a supramaximal stimulation.

 Results: Motor and sensory nerve conduction as well as late response studies were within normal limits, suggesting that none of these patients had any evidence of peripheral neuropathy. Supramaximal electrical stimulation of peripheral nerves at the level of the ankles in the first patient produced a “burning” pain in the feet, which was so intense that she could not control crying during the study.  In the second patient, a single electrical stimulus delivered to the peroneal and tibial nerves produced a ticklish feeling, which elicited uncontrollable laughter on the part of the patient.  In the third patient, electrical studies of median and ulnar nerves produced a dull tapping sensation without any discomfort or dysesthesias.

 Conclusion: Electrical stimulation of mixed peripheral nerves produced a distinctly different sensory response in each of these three patients with FMS. The stimulus parameter used for this study activated only myelinated fibers; small unmyelinated nerve fibers (C-fibers) were not stimulated. The different types of sensations, including burning and a ticklish sensation experienced by our patients, therefore must have resulted from activation of large and small diameter myelinated nerve fibers.  Since the peripheral nervous system was intact in these patients, the perception of burning, tickling, and the dull tapping feeling must be related to abnormalities of central processing mechanisms.

Many of the clinical symptoms of FMS may be related to abnormalities of processing and/or modulating mechanisms in the central nervous system. Depending upon the central mechanism involved, the same stimulus may result in different sensory perceptions. The physiological mechanisms of excitatory postsynaptic potentials (EPSP), inhibitory postsynaptic potentials (FPSP), and presynaptic inhibition, as well as the levels of neurotransmitters and neuromodulation may play a part in producing specific clinical symptoms. Better understanding of these physiological mechanisms will result in better diagnoses and treatment of patients with FMS.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/abnormalities-of-central-processing-mechanisms-in-fibromyalgia/