Numbness is an abnormality in sensory function characterized by diminished or absent sensation. It is usually caused by compression or irritation of a peripheral nerve in the body. The location of the branch of the affected nerve usually determines the site of numbness. It can also be the basis for classifying it. The different types include finger, hand, foot, arm, leg, thigh, and facial numbness.
An abnormality in sensory symptoms can be a positive or a negative phenomenon. This is a term used to denote a negative phenomenon, while paresthesia and dysesthesia are the general terms used to denote a positive phenomenon. Demonstration of numbness upon physical examination indicates that there is damage in at least half of the structure of the peripheral nerve innervating a site or region. Paresthesia refers to tingling or pins-and-needles sensation, whereas dysesthesia generally refers to all types of abnormal sensations whether a stimulus is present or not. Positive phenomena result from an excessive activity in the peripheral or central sensory pathway, and these are not necessarily associated with loss of sensation.
Primary sensation components include pain, thermal sensation, touch, vibration, and joint position. Other terms used for specific sensory abnormalities with negative phenomena are hypesthesia, anesthesia, and hypalgesia or analgesia. Hypesthesia refers to the reduction of pressure, light touch, and warm or cold temperature. Anesthesia refers to the absence of pressure, light touch, warm or cold temperature, and pinprick cutaneous sensation. Hypalgesia or analgesia refers to the reduced or absence of pain perception.
Many nerves innervate different parts of the body. Compression or irritation of a branch of a nerve innervating the hands may cause hand numbness. The same is true with the branch of a nerve innervating other regions of the body.
This condition is generally harmless, but it may occasionally be life threatening. It can be caused by injury to the nerve by trauma, infection, or pressure from tumors or enlarged blood vessels, as well as by certain medications, radiation therapy, and lack of vitamin B12. Medical conditions that cause numbness include diabetes mellitus, multiple sclerosis, carpal tunnel syndrome, migraines, seizures, and stroke. What is important for an individual with this condition is to know when to consult a doctor. If it begins suddenly, involves an entire upper or lower extremity, follows a recent head trauma, or is accompanied with weakness, paralysis, confusion, dizziness, difficulty in talking, sudden or severe headaches, medical care should be sought immediately.