From stiff muscles to painful trigger points to problems with exercise, the muscles can be a problem in fibromyalgia. It turns out that muscles have an interesting way of relaxing when they’re in pain. Every time you contract a painful muscle, your nervous system should take a little break, give your muscles a little break, and reduce your pain.

Rev Bras Reumatol. 2013 Jun;53(3):288-295.Importance of cutaneous silent period in fibromyalgia and its relationship with disease characteristics, psychological disorders and quality of life of patients. Umay EUlas UUnlu EAkgun HCakci AOdabasi Z.

A key neuroprotective process that should kick in when your muscles are in pain appears to be damaged in fibromyalgia

These researchers looked at a curious phenomenon called the ‘cutaneous spinal period’ (CSP) which signifies a period during which the signals from very small sensory  nerves to the brain  get inhibited. Since these sensory nerves (small nerve fibers) carry pain signals to the brain, too much sensory nerve activity is going to leave you in pain.

It turns out that every time you’re in pain and you contract a muscle, in what’s believed to be a protective reflex, that muscle contraction  gets interrupted for a time, and that interruption  can be measured electronically. With all the pain in fibromyalgia these researchers wanted to know how well this pain inhibition process was working in FM. To do that they shocked some muscles in the ‘periphery’ (the body) and the measured the electrical signals they produced.


cutaneous silent period graph

The cutaneous silent period occurs when the electrical signals in a muscle in pain take a pause

Prolonged delays in producing the ‘cutaneous silent period’  indicated that a key protective element is under-performing in FM (and is presumably leaving the muscles in a contracted state for longer than normal periods. ) This is yet another example of a balky pain inhibition process ramping up pain levels in FM.  (Although, the researchers didn’t mention it, one imagines this issue should make pain-free exercise a bit more difficult :).

With a recent study suggesting that the rest period between muscle contractions is pretty much zilch in FM, and this study suggesting the rest period within  muscle contractions are reduced, it’s no wonder people with FM/ME/CFS often experience muscle stiffness and pain.

The very strange phenomenon of sudden body-wide muscle contractions called Stiff Person Syndrome with its interesting associations with FM/ME/CFS  springs to mind as well.

 Small Fiber Neuropathy Implicated

Reduced CSP latency in other disorders (including restless leg syndrome) has been associated with none other than small fiber neuropathy – a hot topic in fibromygalgia right now.  Small fiber neuropathy occurs when small nerve fibers that feed sensory and/or autonomic nervous system data to the brain are damaged by infection, toxins, autoimmune processes, etc. Recent studies suggest a high percentage of people with fibromyalgia may have small fiber neuropathy.

As with other studies, nerve conduction tests indicated the larger nerves were working fine.

Top – Down….Bottom – Up or Both?

The brain sends signals down into these small nerves to inhibit pain signals.  A reduction in the strength of that  pain inhibiting  signal from the brain to the body – probably at the dorsal horn of the spinal cord – could reduce  the cutaneous silent period. Or a small fiber neuropathy could tweak the sensory nerves in the body.


People with fibromyalgia appear to be getting hammered from both ends; the brain and the body

My bet is  that pain inhibition processes in fibromyalgia are getting whacked both from the top – from the brain to the body -and from the bottom – from the body to the brain.

There’s plenty of evidence that the brains on fire, so to speak, in FM.  Two recent studies highlighted a  ‘hyperexcitable’ brainstem and highly activated  brain neurons  have been found in others.  Inhibitory brain chemicals (serotonin) are reduced while excitatory brain chemicals (substance P, glutamate) are increased.

Meanwhile below the brain,  small nerve fiber and blood vessel studies suggest exaggerated  sensory inputs from the body are present.

Every pathway  in the brain and the body that serves to magnify pain in FM appears to be going gangbusters, while the pathways that reduce pain are under-performing. Welcome to the quintessential  pain syndrome in humans.

Given the hyper-excitability present it’s no wonder many of the drugs used in Fibromyalgia and ME/CFS turn down brain activity. Tramadol, interestingly  enough, is able to increase the cutaneous silent period probably through it ability to enhance monaminergic processes involving dopamine, serotonin and norepinephrine.


The finding that pain inhibition at the muscle level is hampered in fibromyalgia  adds to the number of dysregulated pain producing pathways found in fibromyalgia.  The possibility that small fiber neuropathy may be responsible is intriguing given increasing evidence  it may play a major role in FM.

It’s becoming  clearer and clearer that the pain production problems in fibromyalgia are probably global; ie both the brain and the body are implicated…

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