Most of us consider the loss of sensation as numbness but this is only the loss of the sense of touch. Sensation includes the ability to perceive stimuli in the environment and can refer to any of the five senses – touch, taste, smell, hearing and vision. A loss of sensation can therefore also include the inability to taste (ageusia), smell (anosmia), hear (deafness) or see (blindness). The loss of any sensation is concerning and can impact life in a number of ways, especially when it comes to hearing and vision. Understanding why it may occur, what can cause it and the dangers associated with it is therefore important both to prevent it and to seek medical treatment as early as possible.
What is a loss of sensation?
A loss of sensation means that one or more senses are impaired. It can be partial or complete. For example dull or blurred vision is a partial loss whereas blindness is a complete loss of the sense of vision. Our senses provide vital information about our environment to allow us to function and avoid dangers. Although we often take our senses for granted, it involves quite a complex physiologic processes in order for it to function at it optimal.
Loss of sensation is usually a symptom of some underlying disease. These diseases could be acute or chronic. Acute conditions are usually of sudden onset and tend to last for shorter periods of time. Chronic conditions are long term or even permanent and the loss of sensation usually sets in gradually. These conditions may be due to trauma, infections, autoimmune diseases, medication, metabolic disorders and nutritional deficiencies.
Meaning of Loss of Sensation
Any loss of sensation usually means that there is some problem with the organ of sensation, the nerves that carry the signals to the brain or in the centers of the brain that are responsible for deciphering these signals. These organs of sensation rely on nerve endings known as receptors to convert the stimuli into electrical signals that will travel through the nerves to the brain. It may be assisted by other structures, like the entire eye plays a role in vision although it is the rods and cones in the retina that convert light into electrical signals.
Similarly the touch (pressure), temperature, pain and itch receptors in the skin allow us to perceive surface stimuli. Taste buds on the tongue allow for the sense of taste, olfactory receptors in the nasal cavity allow for the sense of smell and the cochlea allows for the sense of hearing. These receptors do not work in isolation but rather in accordance with the surrounding structures where it is housed. Sometimes the sense is not lost or diminished but rather it is malfunctioning where a stimulus or even lack of stimulus is incorrectly perceived.
Causes of Loss of Sensation
One of the most common causes of a loss of sensation is trauma, either to the receptor, nerve or brain centers. This may be seen with injuries like burns that destroy receptors on the skin surface, severed nerve during surgery or a head trauma. There are a number of ways injuries may occurs, from physical trauma associated with falls and assault to chemical trauma as in the case of ingesting certain toxins or electromagnetic injury as is seen with radiation exposure.
Another relatively common cause of acute loss of sensation is infections. Some examples include leprosy caused by Mycobacterium leprae and Lyme disease caused by Borrelia burgdorferi both of which may present with numbness and trachoma caused by Chlamydia trachomatic which leads to blindness. These infections usually lead to the respective loss of sensation by damaging the nerve that carries the impulses of sensation.
Inflammation of an organ of sensation, sensory nerves or brain centers can also lead to loss of sensation. This inflammation may be due to trauma, infections, autoimmune diseases, nutritional deficiencies, metabolic diseases and medication. In some rare instances the inflammation may occur for no clearly identifiable reason. Inflammation is the body’s way of protecting against tissue damage but can disrupt organ function while the inflammation is present.
In autoimmune conditions the immune system may target the organ of sensation or the nerves that carry sensory impulses, thereby leading to inflammation and even destruction of these structures. For example, in neuromyelitis optica the myelin sheath around nerves like the optic nerve are destroyed by the immune system. Sometimes associated structures may be affected which can then impact on sensation. Like in Sjogren’s syndrome the reduced saliva secretion impairs the sense of taste.
One of the more common metabolic disorders that can affect the senses is diabetes mellitus. The elevated blood glucose levels seen in diabetes causes damage to the blood vessels and nerves. Over time this affects both the organ of sensation and nerves. This is more commonly seen in long term and poorly controlled diabetes mellitus. In diabetic neuropathy, the sensation in the limbs in particular are affected. The ability to sense pain, pressure and temperature are severely compromised especially in the legs. Diabetic retinopathy eventually affects vision.
The brain, organs of sensation and nerves all require an adequate blood supply to function effective. Any disease that affects this blood supply will ultimately affect sensation. Strokes are a typical example of a vascular condition that can lead to loss of sensory function when an area of the brain dies due to insufficient blood flow. In the periphery, an occluded artery like with peripheral arterial disease can also lead to a loss of sensation as the nerve tissue is starved off sufficient oxygen and nutrients due to the inadequate blood supply.
Medication and Substances
A number of different drugs can affect the senses. This includes medication like certain antibiotics, antipsychotic drugs, antidepressants, drugs to treat gynecological conditions and antihypertensives (high blood pressure drugs) among others. Similarly a range of non-pharmaceutical substances can cause changes in sensation including alcohol and illicit substances. Toxins like methanol which may be consumed accidentally or intentionally can also affect sensation.
Micronutrients like vitamins and minerals are necessary for healthy functioning of all parts of the body. If any of these nutrients are in low supply then a range of conditions can set in with a host of symptoms. Loss of sensation is one of the common symptoms associated with a deficiency of a number of different micronutrients, including:
- Thiamine (vitamin B1)
- Niacin (vitamin B3)
- Pantothenic acid (vitamin B5)
- Pyridoxine (vitamin B6)
- Folate (vitamin B9)
- Cyanocobalamin (vitamin B12)