Overview and Causes of Smell Disorders

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What are olfactory disorders? What are the causes of dysosmia ( impaired sense of smell ) and why do they occur? Why is this so important?

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Smell and the importance of our sense of smell

It's hard to imagine life without the smell of a rose or the taste of morning coffee. Smell, our sense of smell, plays an important role in almost everyone's life.

Our sense of smell not only helps us to capture the aromas of the air that surrounds us, but it also helps us to enjoy the aromas of food. You may have heard that "taste" has to do primarily with smell, and this is quite true. The impaired sense of smell is very disturbing: the joy of eating and drinking can be lost, which can lead to depression. Additionally, loss of smell is associated with dangers, including the inability to detect gas leaks or spoiled food.

More than 2.7 million people in the United States have an olfactory disorder, and this is probably an underestimate. Some people assume that about half of people over the age of 60 have a reduced sense of smell.

Anatomy and Physiology of Smell (Sense of Smell)

In the upper and middle part of the nose, there is a small cellular area called the olfactory mucosa. This area releases various protective substances such as immunoglobulins (antibodies that bind to foreign bodies such as microorganisms) to prevent pathogens from entering the head. There are also a large number of proteins called receptors that capture chemicals from the environment or perfume. Each receiver is believed to have a specific shape that matches these scents, like a key fits a lock.

Olfactory receptors live in about six to ten million olfactory chemoreceptor cells in each nasal cavity. New receptors are formed throughout adulthood, one of the few examples of how the brain can form new nerve cells throughout life. When there is a correspondence between a chemical in the environment and an olfactory cell receptor, the nerve cell sends a signal directly to the brain through the olfactory bulb.

Although the olfactory bulb is generally considered the "first cranial nerve ," it is not technically a nerve but part of the brain itself. The signals transmitted by the olfactory bulb go to specific parts of the cerebral cortex and even to the amygdala, which is the part of the brain associated with emotions. From the primary olfactory cortex, signals are transmitted to other parts of the brain, including the thalamus and hypothalamus.

Smell disorders

There are several terms that are used to describe different types of olfactory disorders. This includes:

  • Dysomy: impaired sense of smell. Dysosmia, in turn, is classified into two different types of olfactory disorders. Parosmia refers to a change in the perception of smell. Phantosmia, on the other hand, refers to the perception of a smell that does not exist. With parosmia, the smell may be different from what you had in the past, or now you may find a foul odor that you used to like. With phantosmia, you can, for example, smell a fire when there is no fire.
  • Hyposmia: decreased ability to smell.
  • Anosmia: total inability to smell odors.

Causes of disomy (distorted sense of smell)

There are many factors and conditions that can cause dysosmia.

The most common causes are diseases of the nose and sinuses: by blocking the nasal passages and inflammation of the tissues that receive olfactory molecules, viral infections and allergies affect our sense of smell, which almost everyone has experienced at one point or another. Nose-related conditions such as nasal polyps , deviated septum , and surgery and trauma to the nose (such as rhinoplasty) can affect the sense of smell.

Other possible causes include:

  • Head Injury : Traumatic brain injury can affect the sense of smell in different ways: The nose can be damaged, or the nerve fibers that carry information from the nose to the brain can be cut or cut during a head injury. Trauma can also directly damage the olfactory bulb, which detects the molecules we feel.
  • Brain tumors: Both malignant and benign brain tumors , especially those involving the olfactory bulb or temporal lobes, can be associated with changes in the sense of smell. In some cases, loss of smell may be the first symptom of a benign or malignant brain tumor.
  • Toxins in the environment: Tobacco products and smoke impair the sense of smell. Toxins like ammonia, sulfuric acid, and formaldehyde can also reduce the sense of smell.
  • Medications: Certain medications, especially certain classes of medications used to control high blood pressure, can affect your sense of smell. Examples include Procardia (nifedipine), Vasotec (enalapril), and Norvasc (amlodipine).
  • Radiation to the head and neck for cancer
  • Neurological disorders: More than 90 percent of people with Alzheimer's have difficulty smelling and dysosmia is also common in Parkinson's .
  • Diabetes – Similar to the nerve damage that can lead to peripheral neuropathy and retinopathy in diabetes, damage to the nerves involved in smell can also occur.
  • Vitamin deficiency – A zinc or thiamine deficiency leading to Wernicke-Korsakoff syndrome is associated with a loss of smell.

The sense of smell is also often affected, both as a result of natural aging and degenerative diseases such as dementia. While the olfactory bulb in young adults has around 60,000 mitral neurons, both the number of mitral neurons and the diameter of their nuclei decrease dramatically with age.

In about one in five people with olfactory disorders, the cause is "idiopathic," meaning that no specific cause has been found.

Diagnosis of olfactory disorders.

The diagnosis of olfactory disorders often begins with a complete medical history and physical examination. A physical exam can reveal signs of a viral infection or nasal polyps. A careful history can reveal possible toxic effects.

A test known as the University of Pennsylvania odor test can be done to determine if there is indeed hyperosmia or anosmia. Since there are many possible causes ranging from brain disease to nutritional problems and more, further investigation will depend on many factors.

Treat and overcome loss of smell

There are no specific treatments that can reverse the odor change. Sometimes the disomy goes away on its own. Researchers have evaluated the use of high doses of vitamin A and zinc, but so far this does not appear to be effective. Olfactory training is currently being evaluated and appears promising in early research.

Therefore, overcoming difficulties is the main goal of treatment. For those without a sense of smell, safety measures, such as installing a fire alarm, are important. Nutritional advice can be helpful as certain foods and spices can stimulate receptors (trigeminal and smell chemoreceptors).

The bottom line on smell and disorders that affect our sense of smell

In everyday society, the importance of smell and taste is often underestimated. While the olfactory nerve is called the number one cranial nerve, indicating the importance of smell, in practice the sense of smell is rarely tested (even by neurologists). While it is true that the olfactory system of humans is relatively small compared to other mammals, smelling both helps us enjoy life and protect us from environmental toxins.

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