Causes of unilateral numbness

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Unilateral numbness (including tingling or loss of sensation on the surface of the skin) affects the arms and legs. Numbness can occur in the arm, the leg, or both on one side of the body and might also include skin rash, cool or blotchy skin, pain, weakness or fatigue. Symptoms vary depending on the underlying cause. There are several conditions and diseases that cause unilateral numbness.

Herniated Disk

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Herniate means to bulge. When a disk between two bones in the spine presses on nerves around it, it's called a herniated disk and is usually in the lumbar spine (section of spine located between the bottom of your ribs and your hips). Unilateral numbness, along with pain that runs over the buttocks and down the back of one thigh into the calf, is a sign you may have a herniated disk.


Unilateral numbness is a common symptom related to Parkinsonism, which refers to any condition that causes the movement abnormalities found in Parkinson's disease like tremors, slow movement, impaired speech or muscle stiffness. However, having Parkinsonism doesn't mean you have Parkinson's disease. Parkinsonism might be caused by stroke, encephalitis (swelling of the brain), certain medications, or head trauma.

Electrolyte Imbalances

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An electrolyte is a material in the body with free ions that conduct electrical signals. The proper balance of electrolytes is important for regulating everything from oxygen to fluid within your cells. An imbalance can be caused by dehydration (not enough water going into the body) or excessive hydration (too much water in the body). Symptoms include confusion, dizziness and unilateral numbness in the form of weak muscles.

Vitamin B12 Deficiency

Vitamin B12 is needed for the formation of red blood cells, as well as the health of nerve tissue. Vitamin B12 deficiency can result in anaemia and irreversible nerve or brain damage if left untreated. Symptoms of Vitamin B12 deficiency might be subtle at first and include fatigue, palpitations (irregular or heavy heartbeats) and shortness of breath. If left untreated symptoms will worsen and include pale or yellowish skin, diarrhoea, weight loss and vulnerability to infection. If left too long, neurological symptoms begin to show, such as unilateral numbness, trouble walking, irritability, and forgetfulness.


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Unilateral numbness might be due to diabetic neuropathy, a disease of the nervous system that in diabetics usually affects the legs and feet.

Lacunar Infarct

A Lacunar (meaning empty space) infarct (dead tissue) occurs when the small arteries within the brain narrow, causing a lacunar stroke. According to Medicine Net, this blocks the arteries, causing tissue to die. Sudden numbness or weakness in the face, arm or leg, especially on one side of the body, is a common symptom of a lacunar stroke. You might also experience difficulty speaking or understanding, trouble seeing, dizziness, or a sudden severe headache.

Subacute Sclerosing Panencephalitis

Subacute sclerosing panencephalitis (SSPE) is a chronic infection of the central nervous system caused by a variation of the measles virus. It typically affects children and young adults, following a progressive downhill course resulting in death within a few years. According to, there is about a 5 per cent chance of spontaneous remission (sudden improvement). SSPE can occur anywhere from 2 to 10 years after the initial measles illness, and causes neurological deterioration due to swelling in the brain and cell death.

Less Common Causes of Unilateral Numbness

Unilateral numbness might also result from side effects from medications, exposure to chemicals like pesticides, pollutants, alcohol, caffeine, nicotine, or side effects resulting from radiation therapy. Even less common, but possible causes, include migraine headaches, multiple sclerosis, seizures, or underactive thyroid.

Unilateral numbness can signal severe neurological disorders, so if you experience unilateral numbness consult your physician so that he can investigate your medical history and decide on a proper diagnosis and treatment.

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