Burning feet at night

Burning that gets worse when you lie down, worse under the bedcovers, and better when you get up and walk around is a fairly specific pattern with a fairly specific set of causes.

The pattern

People describe it in remarkably consistent ways: a burning or scalding sensation in the soles, sometimes with pins and needles or a feeling of walking on gravel; worse at rest and at night; aggravated by the weight of a sheet; sometimes relieved by putting the feet on a cold floor.

That night-time intensification is characteristic. Nerve pain from the small fibers characteristically gets worse when there is less to distract from it and when the feet are warm, which is exactly what bed provides.

What is usually happening

Most often it is small-fiber neuropathy: injury to the thin, unmyelinated nerve fibers that carry pain and temperature and control sweating and skin blood flow. They are long, metabolically expensive and dependent on a fragile microcirculation, which makes them the first to be affected by high glucose, inflammation and vascular change.

Nerve injury associated with impaired glucose tolerance and metabolic syndrome preferentially affects these fibers, and nerve conduction studies are relatively insensitive to it. That is why the burning-feet-with-a-normal-nerve-test story is so common. Small-fiber versus large-fiber neuropathy.

The other causes worth excluding

Vitamin B12 deficiency — common, easily measured and correctable.
Thyroid disease.
Kidney disease.
Alcohol.
Certain medications, including some chemotherapy agents.
Autoimmune and inflammatory conditions.
Reduced arterial blood flow, which produces a different pattern — typically pain in the foot at night relieved by hanging it out of bed, which is a more urgent finding.

That last one matters. Burning that is relieved by dependency rather than by walking, particularly with a cold or discolored foot or a sore that will not heal, needs prompt assessment rather than a routine appointment.

What can be measured

Sudomotor testing measures small-fiber function through the sweat glands they control, in about three minutes. The vascular study with a toe index answers the circulation question. A laboratory panel covers B12, thyroid, glycemic markers and inflammation. Between them they separate the common causes.

Why the answer matters even when the burning is unchanged

Because the same fibers control sweating. Feet that have stopped sweating develop dry, cracked skin, and cracked skin on a foot that has also lost protective sensation is how a serious wound starts. Identifying that combination changes footwear, foot care and follow-up regardless of what happens to the burning itself. Sudomotor dysfunction.

References

Cortez M, Singleton JR, Smith AG. Glucose intolerance, metabolic syndrome, and neuropathy. Handbook of Clinical Neurology. 2014;126:109–122. doi:10.1016/B978-0-444-53480-4.00009-6
Pop-Busui R, Boulton AJM, Feldman EL, et al. Diabetic Neuropathy: A Position Statement by the American Diabetes Association. Diabetes Care. 2017;40(1):136–154. doi:10.2337/dc16-2042