What is paresthesia?
Paresthesia refers to abnormal sensations in the skin that arise in the absence of any physical stimuli. These abnormal sensations include numbness, itching, burning, pain, and tingling or pins-and-needles sensation. All these sensations may either occur individually or together (example in cases of restless leg syndrome). The abnormal sensations of paresthesia can occur in the skin at any place in the body. It is most common in the extremities such as the hands, legs, face and scalp. Paresthesia can either be temporary and go away on its own or it can be chronic and permanent.
Symptoms of Paresthesias
The symptoms of paresthesia can begin suddenly. Following are some of the common symptoms that are observed in the case of paresthesia:
- Numbness in usually felt in the affected region of the skin. The sensitivity of the skin in the affected region goes down. However, the skin’s sensitivity can also increase in some cases. A common occurrence of such numbness is experienced as a leg or an arm “falling asleep” when it is put under pressure for a long time.
- A tingling feeling (often described as something crawling on the skin) can accompany the numbness in the affected region. Tingling is not to be confused with itching. Unlike an itch, there is seldom any desire to scratch the skin during the tingling sensation.
- Pain may or may not be present.
- The affected area of the skin may feel unusually warm or cool due to alterations in blood supply or sweating that may occur with certain nerve disorders.
- The affected area might be reddish or pale, and may display a swelling or a rash. This depends on the exact cause of the paresthesia.
- A burning sensation might also occur in the affected area.
Each sensory nerve innervates a specific region of the skin in the body. The specific patches of skin that are innervated by individual sensory neurons are known as dermatomes. By determining the distribution of the affected dermatomes in individuals displaying paresthesia symptoms, a doctor can determine the specific nerves that are affected in that individual.
Causes of Paresthesias
The various symptoms of paresthesia occur due to abnormal functions of the sensory neurons that innervate the affected regions of the skin. The sensory information from the skin is carried to the brain for interpretation via the spinal cord and the brainstem. A defect anywhere in this pathway could result in the abnormal sensations of paresthesia.
Paresthesia can either be transient or permanent. Each type is caused by different factors. Transient paresthesia that lasts a few seconds or a few minutes can be caused by the following factors:
- Prolonged pressure on a nerve (example, when keeping legs in a squatting or cross-legged position for a long time) can result in a temporary suspension of sensations from the affected region. This is usually relieved in a few minutes after the pressure on the nerve is released (example., by uncrossing the legs or standing up from a squatting position).
- Panic attacks or hyperventilation could also lead to transient sensations of paresthesia.
- Dehydration can also lead to transient paresthesia.
- A transient ischemic attack (TIA) can also cause a transient paresthesia by affecting the normal functioning of the sensory nervous system.
- Atherosclerosis patients may also report incidences of paresthesia that accompany lack of sufficient blood supply to the legs.
- Deficiency of micro-nutrients (example, calcium, vitamin B12) that are necessary for the maintenance of proper neuronal functions could also lead to symptoms of paresthesia.
- Application of local anesthesics (e.g. in dental procedures) cause a temporary numbness and tingling feeling which goes away after a few hours.
- Seizures in the brain could also temporarily suspend normal sensations, leading to paresthesia.
- Certain viruses, such as herpes simplex virus (HSV), can also cause temporary tingling sensations.
Chronic or permanent paresthesia is a more serious condition that can have a variety of underlying causes:
- Any disease or injury that affects the functioning of the brain, spinal cord, or the sensory nerves can lead to symptoms of paresthesia. Examples of such debilitating conditions include stroke, brain hemorrhage, trauma, multiple sclerosis, meningitis, encephalitis, spinal disc herniation, spondylosis, carpal-tunnel syndrome, repetitive motion injury and neuralgia. Some of these conditions can be life-threatening as well.
- Diseases that affect the circulatory system also affect the proper functioning of the nervous system. Examples of circulatory system disorders that can cause paresthesia include atherosclerosis, angina pectoris, and Raynaud disease. Disorders of the blood (e.g., leukemia, polycythemia, thrombosis, and thrombocytosis) can also cause persistent paresthesia symptoms.
- Disorders of the vertebral column, such as herniated discs, could also lead to sensations of paresthesia by compressing the spinal nerves.
- Metabolic and hormonal disorders that cause chronic paresthesia include hypothyroidism, diabetes, Conn’s syndrome and low blood sugar.
- Another category of diseases that can lead to paresthesia include autoimmune disorders. Examples include rheumatoid arthritis, pernicious anemia, diabetes, and systemic lupus erythematosus.
- Chronic nutritional deficiencies of neuroprotective B-complex vitamins (vitamins B1, B5 and B12) can also lead to long term paresthesia.
- Certain tumors, either in the brain or elsewhere in the body, can affect the normal functioning of the sensory nervous system. This could lead to abnormal sensations either due to improper signaling by the nerves or due to improper interpretation of sensory signals in the brain.
- Serious trauma to the skin caused by burns and frostbites also affect the normal sensations in the skin.
- Long term consumption of certain drugs (example., lomotil, anti-convulsant medicines, and SSRI) and toxins (e.g., tetrodotoxin in puffer fish) can cause chronic paresthesia.
- Damage to the skin and the sensory nerves caused by radiotherapy and chemotherapy is also a cause of paresthesia.
- Hereditary disorders such as Refsum’s disease, Charcot-marie-tooth disease, ataxia telangiectasia, and Fabry’s disease also contribute to incidences of chronic paresthesia.
Treatment for Paresthesias
Paresthesia that is temporary usually goes away on its own upon restoration of proper sensory nerve functioning. For chronic paresthesia, the underlying cause of the abnormal sensations need to be discovered before a specific line of treatment can be prescribed by the doctor. Treatment may require a combination of medication, surgery and other treatments such as physical therapy.