Temperature Insensitivity

How temperature sensation works

Temperature is detected by small nerve endings in the skin. Signals travel along thin nerve fibers (A-delta for cold, C fibers for warmth and pain) to the spinal cord, where they cross to the opposite side and travel up the spinothalamic tract to the brain. Damage anywhere along this path reduces the ability to feel hot or cold. Because pain uses the same fibers and pathways, people who cannot feel temperature often also feel less pain.

Causes of temperature insensitivity

Peripheral neuropathy (most common)

Damage to the nerves outside the brain and spinal cord usually starts in the toes and feet and slowly spreads upward in a "stocking and glove" pattern.

• Diabetic neuropathy: affects up to half of people with long-standing diabetes. Early on it often affects small fibers first, so loss of temperature and pain sense, with burning or tingling, can come before numbness to touch
• Vitamin B12 deficiency: from pernicious anemia, a vegan diet, metformin or acid-reducing medicines
• Alcohol-related neuropathy
• Chemotherapy (platinum drugs, taxanes, vincristine) and some other medicines
• Underactive thyroid, kidney failure, HIV, celiac disease and autoimmune conditions
• Prediabetes: can cause small-fiber neuropathy before diabetes is diagnosed

Spinal cord causes

• Syringomyelia: a fluid-filled cavity in the spinal cord interrupts the crossing temperature and pain fibers. It causes a classic "cape" distribution of lost temperature sense across the shoulders and arms, while light touch is preserved. People often notice painless burns on their hands
• Spinal cord injury, tumors and compression
• Multiple sclerosis and other inflammatory spinal cord conditions

Brain causes

A stroke in the brainstem or thalamus can cause loss of temperature and pain sense on one side of the body, sometimes with the opposite side of the face.

Nerve injuries

Cuts, compression or surgery affecting a single nerve cause loss of sensation in that nerve's area. Shingles can leave patches of altered sensation.

Inherited conditions

Hereditary sensory and autonomic neuropathies and congenital insensitivity to pain are rare genetic conditions in which children cannot feel pain or temperature properly, leading to repeated injuries.

Skin damage

Scars, burns and frostbite can damage nerve endings in the affected area.

Patterns that point to the cause

Other symptoms that may come with it

• burning, tingling or electric pains, often worse at night
• numbness to touch and vibration
• loss of balance, especially in the dark
• painless sores, burns or calluses on the feet
• dry, cracked skin and changes in sweating
• weakness or muscle wasting in more advanced cases

How doctors diagnose the cause

A doctor will test temperature sensation with cold and warm objects (such as a tuning fork or metal rod), pinprick, light touch, vibration and position sense, and check reflexes and strength. The pattern of loss helps locate the problem.

Tests may include:

• Blood tests: HbA1c or glucose tolerance test, vitamin B12, thyroid function, kidney function, and others depending on history
• Nerve conduction studies: detect large-fiber neuropathy, but are often normal in pure small-fiber neuropathy
• Skin biopsy: counts small nerve fibers to confirm small-fiber neuropathy
• Quantitative sensory testing: measures temperature thresholds precisely
• MRI of the spine or brain for syringomyelia, spinal cord or stroke causes

Treatment

Treatment focuses on the cause and on preventing injury.

Treat the cause

• Tight blood sugar control in diabetes slows nerve damage
• B12 injections or tablets for deficiency
• Stopping alcohol, with good nutrition and thiamine
• Reviewing medicines that damage nerves
• Surgery to drain a syrinx or relieve spinal cord compression when appropriate
• Stroke treatment and rehabilitation

Protect yourself from burns and cold injuries

• Check bath and shower water with a thermometer (aim for no hotter than about 37 to 38 °C or 98 to 100 °F) or your elbow, if your elbow sensation is normal
• Set your water heater to 49 °C (120 °F) or lower
• Never use hot water bottles, heating pads or electric blankets on numb skin
• Do not warm feet by a fire or heater
• Wear insulated gloves and socks in cold weather and limit time outdoors to prevent frostbite
• Use oven gloves and be careful with hot drinks and pans

Foot care

• Check your feet every day for blisters, cuts, redness and swelling, using a mirror if needed
• Wear well-fitting shoes and socks, and never walk barefoot
• See a podiatrist regularly if you have diabetes or neuropathy

Nerve pain relief

If burning or shooting pain comes with the loss of sensation, prescription medicines such as duloxetine, pregabalin, gabapentin or amitriptyline can help.

Frequently asked questions

Why can't I feel hot or cold?

The commonest reason is damage to the small nerve fibers that carry temperature, usually from diabetes. Other causes include vitamin B12 deficiency, alcohol, chemotherapy, spinal cord problems such as syringomyelia, multiple sclerosis and stroke. A doctor can find the cause with an examination and tests.

Is loss of temperature sensation serious?

It can be, both because of its cause and because it raises the risk of burns, frostbite and unnoticed foot ulcers. Sudden loss on one side of the body may be a stroke and is an emergency. Gradual loss should be investigated by a doctor.

Can diabetes cause you to not feel hot water?

Yes. Diabetic neuropathy often affects temperature sensation in the feet first, so people may not notice that bath water is too hot. Check water with a thermometer, and inspect your feet daily for blisters or burns.

Can loss of temperature sensation be reversed?

Sometimes. Treating B12 deficiency early, stopping alcohol, improving blood sugar control and treating spinal cord causes can lead to partial recovery. Long-standing nerve damage often does not fully recover, but treatment can stop it getting worse.