Why do we sometimes get 鈥減ins and needles鈥�, especially in our arms and legs, and what exactly occurs in our bodies to make this happen?
鈥� Pins and needles, properly called paraesthesia, can be caused by a number of things. The commonest cause is direct compression of a sensory nerve, inhibiting its ability to send sensory information to the brain. This often occurs where a nerve runs close to the body surface and on top of a bone. For example, compression of the ulnar nerve as it crosses the elbow causes pins and needles in the hand. This is why people wake up with pins and needles: they have compressed a peripheral nerve by lying on it.
Less commonly, abnormal plasma calcium levels can cause pins and needles, also by affecting sensory nerve function. Low calcium, sometimes seen after thyroid surgery, classically causes pins and needles in the hands. Hyperventilation also causes the sensation by making the blood more alkaline, thus driving calcium into cells and lowering plasma calcium. Pins and needles in the feet is a sign of nerve damage caused by poorly controlled diabetes.
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Sinister causes of pins and needles include neurological conditions such as stroke and multiple sclerosis. The short answer, therefore, is that pins and needles is caused by some factor impairing sensory nerve function.
鈥淪inister causes of pins and needles include neurological conditions such as stroke鈥�
David Anderson, Hawkes Bay Regional Hospital, Hastings, New Zealand
鈥� Paraesthesia describes a number of abnormal sensations, including pins and needles. Transient paraesthesia is the temporary sensation of tingling, pricking or numbness of the skin and has no apparent long-term effect.
It is commonly felt in the extremities and is usually caused by a lack of blood supply or by inadvertent pressure placed on a superficial nerve.For example, if you kneel or sit on your legs, the weight of your body tends to limit the blood supply to the lower limb and as a result, the nerves become starved of blood, and start to send unusual signals to the brain. This is perceived as a tingling sensation or pins and needles in the foot or lower leg. Once you move and change position, the nerve compression is released and the pins and needles gradually fade.
Paraesthesia may also be chronic. Poor circulation is common in older people. It may be caused by conditions such as atherosclerosis or peripheral vascular disease. Without a sufficient blood supply and hence nutrients, nerve cells cannot function normally. This is also why paraesthesia can be a symptom of malnutrition, as well as metabolic disorders such as diabetes and hypothyroidism.
Additionally, inflammation of tissue can irritate nerves running through it, causing paraesthesia. This is the case in conditions such as carpal tunnel syndrome and rheumatoid arthritis. Chronic paraesthesia can sometimes be symptomatic of neurological disorders such as motor neurone disease or multiple sclerosis.
Melanie Trickett, Bristol, UK