Ask Dr James: Why do the soles of my feet feel like they’re burning?
Q: “I have a mixture of pain and burning in the soles of both my feet. This is not much of an issue during the day when I’m moving about, but in bed the burning can stop me dropping off and wake me every couple of hours. It is most troublesome.”
A: The discomfort of burning feet is directly comparable to the effect of their being in too close proximity to an electric heater or radiator. Caused by disturbed functioning of the sensory nerve fibres (sensory neuropathy), it is indeed, as can be readily imagined, “most troublesome”.
The skin is a highly sensitive organ packed with millions of miniscule sensory receptors conveying the subtleties of touch while also alerting us to potentially damaging extremes of temperature (both heat and cold), excessive pressure and the presence of injury-inducing chemicals. When activated, these specialised receptors convert noxious stimuli into electrical impulses, conveyed from the feet up to the spinal cord along the sensory nerves. These, the longest in the body, are vulnerable to the wear and tear of passing years, experienced variously as shooting pains, pins and needles, and burning.
A treatable underlying cause?
The first consideration is whether there might be some treatable underlying explanation, starting with vitamin B deficiency – rare nowadays but prevalent among heavy drinkers and the severely malnourished. “Burning feet are a source of terrible discomfort preventing sleep and rest,” wrote the famed Australian doctor “Weary” Dunlop of his fellow Japanese POWs on the notorious Thai-Burma Death-Railway. Vitamin B supplements are usually curative.
Next, diabetes, the single commonest cause of sensory neuropathy, mitigated by adequate control with blood-sugar-lowering drugs. The third possible treatable cause is rather different – compression of the tibial nerve around the ankle, known as tibial tunnel syndrome. Similar to carpal tunnel syndrome at the wrist, this may improve with physiotherapy and local steroid injections, but for some an operation to decompress the nerve may be necessary.
Cooling the feet
There is inevitably no specific remedy that can correct the disturbed functioning of the sensory nerves, though the threshold for activation of those heat-sensitive receptors can be raised by cooling the feet in a water bath. A “cold” hot-water bottle tucked into the side of the bed until needed can be similarly useful. “When woken by burning in the night, it provides much welcome relief,” a woman reports.
Medication
The two classes of drugs that may mitigate the burning sensation are, first, the local anaesthetic lidocaine or chilli-derived capsaicin that, applied as a gel or patch, inhibit the firing of those heat-sensitive receptors in the skin. Next, the therapeutic effect of several classes of drugs depends on their “damping down” the transmission of the electrical impulses – gabapentin (epilepsy), amitriptyline (depression) and mexiletine (abnormal heart rhythms). Despite the rationale for their use in mitigating the discomfort of burning feet, the evidence for their efficacy is equivocal, with at best a 50 per cent improvement in a quarter of those taking them.
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