Paresthesias

Paresthesia ( or ), is a sensation of tingling, tickling, prickling, pricking, or burning of a person's skin with no apparent long-term physical effect. The manifestation of a paresthesia may be transient or chronic.

The most familiar kind of paresthesia is the sensation known as "pins and needles" or of a limb "falling asleep". A less well-known but still fairly common paresthesia is formication.

Etymology
The word paresthesia comes from the Greek para ("beside", i.e., abnormal) and aisthesia ("sensation").

Transient
Paresthesias of the hands and feet are common, transient symptoms of the related conditions of hyperventilation syndrome, often open mouth, and panic attacks.

Other common examples occur when sustained pressure has been applied over a nerve, inhibiting/stimulating its function. Removing the pressure typically results in gradual relief of these paresthesias.

Chronic
Chronic paresthesia indicates a problem with the functioning of neurons or poor circulation.

In older individuals, paresthesia is often the result of poor circulation in the limbs (such as in peripheral vascular disease, also referred to by physicians as PVD or PAD), most often caused by atherosclerosis, the build up of plaque within artery walls, over decades, with eventual plaque ruptures, internal clots over the ruptures and subsequent clot healing but leaving behind narrowing of the artery openings or closure, both locally and in downstream smaller branches. Without a proper supply of blood and nutrients, nerve cells can no longer adequately send signals to the brain. Because of this, paresthesia can also be a symptom of vitamin deficiency and malnutrition, as well as metabolic disorders like diabetes, hypothyroidism, and hypoparathyroidism. It can also be a symptom of mercury poisoning.

Irritation to the nerve can also come from inflammation to the tissue. Joint conditions such as rheumatoid arthritis, psoriatic arthritis, and carpal tunnel syndrome are common sources of paresthesia. Nerves below the head may be compressed where chronic neck and spine problems exist and can be caused by, among other things, muscle cramps that may be a result of clinical anxiety or excessive mental stress, bone disease, poor posture, unsafe heavy-lifting practices or physical trauma such as whiplash. Paresthesia can also be caused simply by putting pressure on a nerve by applying weight (or pressure) to the limb for extended periods of time.

Another cause of paresthesia, however, may be direct damage to the nerves themselves, i.e., neuropathy, which itself can stem from injury or infection such as frostbite or Lyme disease, or may be indicative of a current neurological disorder. Neuropathy is also a side effect of some chemotherapies. Benzodiazepine withdrawal may also cause paresthesia as the drug removal leaves the GABA receptors stripped bare and possibly malformed. Chronic paresthesia can sometimes be symptomatic of serious conditions, such as a transient ischemic attack, or autoimmune diseases like multiple sclerosis or lupus erythematosus.

The herpes zoster disease (shingles) can attack nerves causing numbness instead of pain commonly associated with shingles. A diagnostic evaluation by a medical doctor is necessary to rule these out.

Demyelinating diseases may also cause cross-talk between adjacent axons and lead to paresthesia. During impulse conduction some aberrant current that escaped a demyelinated axon can circulate in the exterior and depolarize an adjacent demyelinated, hyperexcitable axon. This can generate impulses conducted in both directions along this axon since no part of the axon is in a refractory state. This becomes very serious in conditions such as multiple sclerosis and Guillain–Barré syndrome.

Acroparesthesia
Acroparesthesia is severe pain in the extremities, and may be caused by Fabry disease, a type of sphingolipidosis.

Dentistry
Paresthesia or "persistent anesthesia" is a transient or potentially permanent condition of extended numbness after administration of local anesthesia and the injected anesthetic has terminated.

Potential causes include trauma induced to the nerve sheath during administration of the injection, hemorrhage about the sheath, type of anesthetic used, or administration of anesthetic potentially contaminated with alcohol or sterilizing solutions.

Other
Other causes may include:


 * anticonvulsant pharmaceutical drugs, such as topiramate, sultiame, and acetazolamide
 * anxiety and/or panic disorder
 * benzodiazepine withdrawal syndrome
 * carpal tunnel syndrome
 * chiari malformation
 * complex regional pain syndrome (CRPS), also known as reflex sympathetic dystrophy (RSD)
 * beta-alanine
 * beta blocker
 * celiac disease
 * decompression sickness
 * dehydration
 * dextromethorphan (recreational use)
 * Fabry disease
 * Erythromelalgia
 * fibromyalgia
 * Fluoroquinolone Toxicity
 * Guillain–Barré syndrome (GBS)
 * heavy metals
 * hydroxy alpha sanshool, a component of Sichuan peppers
 * hyperglycemia (high blood sugar)
 * hyperkalemia
 * hyperventilation
 * hypoglycemia (low blood sugar)
 * Hypomagnesemia, often as a result of long term Proton-pump inhibitor use
 * hypothyroidism
 * immunodeficiency, such as chronic inflammatory demyelinating polyneuropathy (CIDP)


 * intravenous administering of strong pharmaceutical drugs acting on the central nervous system (CNS), mainly opioids, opiates, narcotics; especially in non-medical use (drug abuse)
 * lidocaine poisoning
 * Lomotil
 * Lyme disease
 * menopause
 * mercury poisoning
 * migraines
 * multiple sclerosis
 * nitrous oxide, long-term exposure
 * obdormition
 * pyrethrum and pyrethroid (pesticide)
 * rabies
 * radiation poisoning
 * sarcoidosis
 * spinal disc herniation or injury
 * stinging nettles
 * syringomyelia
 * transverse myelitis
 * vitamin B5 deficiency
 * vitamin B12 deficiency
 * withdrawal from certain selective serotonin reuptake inhibitors (or serotonin-specific reuptake inhibitors) (SSRIs), such as paroxetine or serotonin-norepinephrine reuptake inhibitors (SNRIs) such as venlafaxine

Diagnostic approach
The nerve conduction study usually provides useful information for making diagnosis. A CT scan is sometimes used to rule out some causes from the central nervous system.

Treatment
Medications offered can include the immunosuppressant prednisone, intravenous gamma globulin (IVIG), anticonvulsants such as gabapentin or Gabitril and antiviral medication, among others, according to the underlying cause.

In addition to treatment of the underlying disorder, palliative care can include the use of topical numbing creams, such as lidocaine or prilocaine. Care must be taken to apply only the necessary amount, as excess can contribute to the condition. Otherwise, these products offer extremely effective, but short-lasting, relief from the condition.

Paresthesia caused by shingles is treated with appropriate antiviral medication.