Numbness and Paresthesia
In Chinese medicine, numbness and paresthesia are caused by a lack of blood flow to the skin. The skin relies on a constant supply of blood to maintain its elasticity and sensitivity. When blood flow is inadequate or blocked by a pathogen, numbness and paresthesia can occur. In general, numbness is caused by a pathogen blocking the blood flow, while tingling and pins and needles are caused by a deficiency in blood flow. However, in practice, various degrees of numbness and tingling may be seen together.
In biomedicine, there are two main causes of numbness and paresthesia: mechanical compression or damage to a sensory nerve, or nerve damage from metabolic issues, ischemia, autoimmune disorders, infections, or nutritional deficiencies.
Protective qi is a concept in traditional Chinese medicine (TCM) that refers to the body's ability to defend itself against external pathogens. When this qi is weak, the body is more susceptible to invasion by pathogens. This can lead to a blockage in the distribution of qi and blood, resulting in symptoms such as tingling or numbness. In TCM, external wind is thought to be a cause of these symptoms, particularly in the trunk and proximal limbs.
Dampness is another concept in TCM that refers to a type of pathogen that can cause a heavy, wooden feeling in the tissues, particularly in the lower limbs. This is more likely to occur in people who have been exposed to prolonged damp conditions. Dampness is thought to cause sensory loss and a gradual onset of symptoms, as it seeps into the tissues.
Qi and Blood Deficiency
In TCM, the Spleen is thought to play a key role in supplying qi and blood to the skin. When the Spleen is weakened, either due to an inadequate diet or other factors, the supply of qi and blood to the skin is reduced. This can lead to a deficiency of qi, which in turn can cause a deficiency of protective qi. This makes the body more susceptible to invasion by external pathogens.
Other factors that can contribute to qi and blood deficiency include overwork, prolonged breastfeeding, and loss of qi and blood from hemorrhage during childbirth. These factors can weaken the Spleen and lead to reduced supply of qi and blood to the skin. In TCM, this can manifest as symptoms such as paresthesia and numbness.
In TCM, numbness and paresthesia can be caused by two mechanisms: failure of yin to nourish the tissues and failure of yin to restrain yang. Both of these mechanisms are associated with a decline in yin, which can be caused by aging, fever, chronic disease, heating diet, chronic damp-heat, drug use, or qi and blood deficiency.
When yin deficiency is the main cause of numbness and paresthesia, it is usually part of a deeper pattern of disharmony involving the sinews and bones. This can manifest as weakness, stiffness, possible pain and atrophy, dryness and thinning of skin, and loss of sensitivity.
In the case of yin deficiency leading to ascendant yang and internal wind, symptoms may include relatively acute onset of numbness affecting the extremities, upper body, and face, as well as vertigo, tinnitus, and headaches. This may be a warning sign of an impending wind-stroke, a condition in TCM that is thought to be caused by a sudden rise of wind in the body.
In TCM, phlegm is thought to be caused by the congealing of normal physiological fluids or dampness. It can be either constitutional or introduced through the diet. Phlegm can cause numbness and paresthesia by congealing in the tissues, obstructing the collaterals and hindering the circulation of qi and blood.
Phlegm can be produced in a number of ways. For example, it can be formed when fluids are slowed and congested by constrained qi, or when fluid metabolism is poor due to weakness in the Lungs, Spleen, and Kidneys. Phlegm can also be produced by the condensing of fluids due to heat, damp-heat, or qi constraint, or by yin deficiency.
Chronic accumulation of dampness in the tissues from rich, fatty, sweet foods, persistent overeating, or exposure to cold, raw foods that weaken the Spleen can also gradually thicken into phlegm. In TCM, this can lead to a range of symptoms, including numbness and paresthesia.
Numbness and paresthesia can be caused by blood stasis, which is a condition in which blood flow is slowed or impeded. This can occur as a result of physical trauma or surgery, as well as chronic conditions such as liver qi constraint, cold, phlegm, damp-heat, or deficiency of yang qi, blood, or yin. Prolonged inactivity, an awkward sleeping position, sitting in one position for extended periods, heavy cigarette smoking, and dehydration can also contribute to blood stasis and numbness. In general, blood stasis causes a complete loss of sensation and a feeling of stiffness in the affected tissues.
Numbness and paresthesia can be caused by the impingement of sensory nerves as they exit the spinal cord or along their pathway. Causes of this impingement include the narrowing of the gap between vertebrae due to the thinning of the intervertebral disc, the growth of osteophytes, or muscle spasm. When specific nerves are compressed, numbness and paresthesia can present in the relevant dermatome. Temporary nerve compression can also cause numbness and paresthesia. For example, numbness in the hands and fingers that wakes people from sleep may be caused by constriction of the brachial plexus as it passes through the scalene muscles in the lateral neck or under the attachment of pectoralis minor in the anterior shoulder by an awkward sleeping position. The ulnar nerve can be compressed where it navigates the elbow joint, and sensory change in the middle three fingers can be due to compression of the median nerve as it passes through the carpal tunnel. These types of numbness can be mechanical, but they can also be caused by Chinese-medically defined pathologies such as liver qi constraint or spleen qi deficiency.