Dan Clauw recently wrote an insightful editorial for Pain[1], in which he highlighted an important finding about the idea that people with fibromyalgia show signs of ‘small fibre neuropathy’. Changes in intra-epidermal nerve fibres (‘small fibres’) have been shown in many clinical conditions, including conditions that are characterised by chronic pain. So the idea that people with fibromyalgia show such changes is not revolutionary. However, the study Clauw refers to also examined the nature of the changes, comparing small fibre biopsies in people with fibromyalgia to healthy controls and to people with the classic signs and symptoms of ‘small fibre neuropathy’[2]. Unsurprisingly, the nature of the changes in fibromyalgia differ from those in classic small fibre neuropathy, which the authors interpreted as suggesting that the mechanisms driving the changes probably differ, too.
Clauw uses this as a springboard to point out that naming these differences in intra-epidermal nerve density as ‘small fibre neuropathy’ in those that don’t have the classic set of signs and symptoms of small fibre neuropathy is likely to cause confusion, because (a) it implies a causative link and (b) it ignores the subtle, but relevant, heterogeneity in morphology. There is sufficient evidence to firmly support the view that chronic pain conditions like fibromyalgia cannot be caused exclusively by peripheral disease: the central nervous system appears to be a major player. Indeed, it is far more likely that the central nervous system drives the changes in intra-epidermal nerve fibres (concomitant with probable changes in many other peripheral structures) that are seen in people with fibromyalgia and in other chronic pain conditions.
So what words should we use to describe these small fibre changes that seem nearly ubiquitous in chronic pain conditions? If we view the many central changes that are seen in chronic pain conditions as evidence of ‘neuroplasticity’, why do we not take the same view for peripheral changes? After all, Clauw argues, it is plausible that the changes in small fibres could be a response to a myriad of drivers. Whatever term we use ought to allow for the possibility that morphological changes in intra-epidermal nerve fibres are a side event to the main show; they may only be relevant if and when they match up with a patient’s history and clinical findings.
About Tory Madden
Tory arrived from South Africa to start her PhD at BiM. She is a physiotherapist who worked clinically before turning her focus toward research. She is interested in pretty much anything related to pain and neuroscience, thanks to some particularly inspirational teaching by Romy Parker during her undergraduate training at the University of Cape Town.
Tory’s research looks at classical conditioning and pain. She is also an associate editor for BiM. She tries to spend much of her spare time exercising to compensate for the vast quantity of chocolate that lives in her bottom desk drawer. Luckily, she loves trail running as much as she does food.
References
[1] Clauw, Daniel J. (2015) What is the meaning of “small fiber neuropathy” in fibromyalgia? Pain 156:2115-16.
[2] Doppler, Kathrin; Rittner, Heike L.; Deckart, Maximiliane; Sommer, Claudia (2015) Reduced dermal nerve fiber diameter in skin biopsies of patients with fibromyalgia. Pain 156:2319-25.