Loss of Sensation (Numbness): Causes by Pattern

What loss of sensation means

"Loss of a sensation or feeling" in medical terms is hypoesthesia (reduced feeling) or anesthesia (no feeling at all). Specific types have their own names:

• Hypoalgesia or analgesia: reduced or absent pain sensation.
• Thermanesthesia: loss of temperature sense.
• Pallanesthesia: loss of vibration sense.
• Loss of proprioception: not knowing where a limb is without looking, which causes unsteadiness in the dark.

Loss of sensation is different from paresthesia, which is an abnormal added sensation such as tingling or pins and needles. The two often occur together. For a plain-language overview of numbness, how it feels and how to protect numb skin, see loss of feeling.

Causes by pattern

The shape of the numb area is the most useful clue to where the problem is.

Brain and spinal cord causes

• Stroke and TIA: sudden numbness on one side, often with weakness, facial droop or speech difficulty.
• Multiple sclerosis: patches of numbness that develop over days and may come and go, often with vision problems or fatigue. Bending the neck may cause an electric shock down the spine (Lhermitte's sign).
• Spinal cord compression from a disc, tumor, abscess or fracture.
• Migraine aura: numbness that spreads slowly over 5 to 20 minutes, usually from the hand to the face, followed by headache.
• Seizures that start in the sensory part of the brain.

Nerve root causes

A herniated disc or narrowed spinal canal can squeeze a nerve root, causing numbness in a strip of skin (a dermatome) down the arm or leg, usually with shooting pain. Sciatica is the best-known example. Shingles can also cause numbness in a band after the rash.

Single nerve causes (mononeuropathy)

• Carpal tunnel syndrome: thumb, index, middle and half the ring finger, worse at night.
• Cubital tunnel syndrome: little finger and half the ring finger, worse with the elbow bent.
• Peroneal nerve palsy: numb top of the foot with foot drop, often after crossing the legs or weight loss.
• Meralgia paresthetica: burning numbness on the outer thigh from a pinched nerve at the hip, linked to tight belts and weight gain.

Widespread nerve damage (polyneuropathy)

Peripheral neuropathy usually starts in the toes and spreads upward, because the longest nerves are affected first. Causes include:

• diabetes, the most common cause in the US
• vitamin B12 deficiency, including from metformin, acid-suppressing drugs or a vegan diet
• heavy alcohol use
• chemotherapy and some other drugs
• underactive thyroid, kidney disease and HIV
• inherited neuropathies such as Charcot-Marie-Tooth disease

Sudden onset of loss of sensation

Sudden numbness, developing in seconds to hours, usually means a vascular, compressive or inflammatory cause: stroke, a blocked artery to a limb, a nerve compressed during sleep, an acute disc herniation or Guillain-Barre syndrome (which usually starts with tingling feet and rising weakness). Sudden numbness always deserves prompt assessment, and one-sided numbness of the face, arm or leg is an emergency.

How doctors find the cause

A doctor will ask when it started, where exactly it is, whether it is spreading, and about weakness, pain, bladder or bowel changes, diabetes, alcohol, medicines and diet. The examination tests light touch, pinprick, temperature, vibration with a tuning fork and position sense, plus reflexes and strength, to map the affected area.

Tests may include:

• blood tests: glucose and HbA1c, B12, thyroid, kidney and liver function, and protein electrophoresis
• nerve conduction studies and electromyography (EMG)
• MRI of the brain or spine
• CT of the head urgently if a stroke is suspected

Treatment and protecting numb areas

Treatment depends on the cause: emergency stroke treatment, surgery for cord or cauda equina compression, wrist splints or surgery for carpal tunnel syndrome, B12 replacement, blood sugar control, or stopping a drug or alcohol.

While feeling is reduced, protect the area:

• Test bath water with your elbow or a thermometer.
• Check numb feet every day for cuts, blisters and redness, and wear well-fitting shoes.
• Avoid heating pads and hot water bottles on numb skin.
• Use night lights and remove tripping hazards if position sense is affected.

Frequently asked questions

What is the medical term for loss of sensation?

Reduced sensation is called hypoesthesia, and complete loss is called anesthesia. Loss of pain sensation is hypoalgesia or analgesia. Abnormal sensations such as tingling are called paresthesias. In everyday language, all of these are often described as numbness.

What causes a sudden loss of sensation?

The most urgent cause is a stroke or TIA, especially when numbness is on one side of the body. Other causes include a nerve compressed during sleep, a herniated disc, a blocked artery to a limb, Guillain-Barre syndrome, migraine aura and multiple sclerosis. Sudden one-sided numbness needs a 911 call.

Is loss of sensation the same as numbness?

Mostly, yes. Numbness is the everyday word for reduced or absent feeling. Some people also use "numb" to describe tingling, heaviness or weakness, so doctors ask detailed questions and examine sensation directly to work out what is really happening.

Can loss of sensation come back?

Often it can. Sensation usually returns after a compressed nerve is relieved, B12 is replaced or a disc settles, though nerves regrow slowly, around 1 mm a day. Long-standing nerve damage from diabetes or a severe injury may only partly recover.

Can anxiety cause loss of sensation?

Anxiety and panic attacks can cause tingling and numbness, typically around the mouth and in both hands, from over-breathing. It fades as breathing settles. One-sided numbness, numbness with weakness, or numbness that does not go away should not be put down to anxiety without a medical assessment.