Parageusia: Pathophysiology, Causes, Symptoms, Treatment, Diagnosis
What is Parageusia?
Parageusia is a type of taste disorder where a person experiences changes in taste in the mouth, especially has bad taste. Parageusia is a condition where a person has bad taste in the mouth. Parageusia also includes change in taste and wrong perception of particular tastes. Metallic taste of food is a common type of parageusia, which can occur as a side effect to many medications.
Parageusia can be permanent or it can be temporary. Temporary Parageusia can occur from infections, such as influenza, sinusitis, common cold, pharyngitis, respiratory infection, ear infection etc. Permanent Parageusia can occur from nerve damage.
For treating parageusia, it is important to find the cause of parageusia or the source of the bad/altered taste.
Classification of Taste Disorders
Taste disorders are categorized into: Parageusia, Hypogeusia, Dysgeusia and Ageusia.
- Parageusia is a condition where a person has bad taste in the mouth.
- Dysgeusia is a condition where there is a change in the taste that can be present beyond the meal. Dysgeusia can also be accompanied by glossitis, burning mouth syndrome and other oral health problems.
- Hypogeusia is a condition where there is decreased sense of taste in the mouth.
- Ageusia is a taste disorder where there is absence of any taste, i.e. the person is not able to detect any taste at all. Ageusia is very rare.
Pathophysiology of Parageusia
The sense of taste is communicated to the brain through the taste buds. Taste buds are present on the tongue and the roof of the mouth and they consist of cells, which collect information about taste. Taste buds have the ability to identify only the following tastes: sour, salty, bitter, sweet and umami (recently discovered). Other more subtle tastes and flavors can be experienced through smell. So, in some cases if a person thinks there is a problem with his/her taste, it could actually be a problem with the person's smell.
The surface of tongue contains the taste receptor cells. There are 5 types of tastes recognized by the taste buds which include sour, sweet, salty, bitter, and umami. Umami is a recently discovered taste sensation. The taste buds contain the taste receptor cells, which are a cluster of cells present in a spherical manner. A pore is present on the surface of the taste bud. The microvilli of the receptor cells project into this pore. Taste buds are present in the papillae that are present on the dorsum of the tongue and along the lateral margin of the tongue, at the junction of the base of the tongue; in the palate, larynx, epiglottis and esophagus. The glossopharyngeal, facial and vagal nerves transmit the sense of taste to the brain. There are 3 types of taste receptors.
- First one is which identifies the salty taste.
- Second one is which identifies the sweet, bitter and umami, taste.
- Third is which identifies the sour taste.
When a person takes a bite of the food, it gets mixed with the saliva and interacts with the taste receptors which results in a chemical reaction. This causes transmission of afferent signals to the cerebral cortex of the brain about the taste.
Causes of Parageusia
There are various causes for taste disorders including parageusia. Some of the causes include damage to the taste buds, drug side effects, nerve problems, infections and other health problems. Most of the causes of parageusia are temporary and reversible. Common causes of parageusia include:
Infections: Infections, such as influenza, sinusitis, pharyngitis, ear infection, tonsillitis, common cold, nasal infection, respiratory infection, oral yeast infection and salivary gland infection can cause parageusia.
Medicines: Certain medicines can also cause taste changes including parageusia. Some of the taste disrupting drugs include: HIV/AIDS drugs; cancer treatment; warfarin (blood thinner); lithium (mood stabilizer); venlafaxine (antidepressant); propafenone (anti-arrhythmic); alendronate (for osteoporosis); metformin (for diabetes & obesity); topiramate (anticonvulsant); olopatadine (antihistamine); morphine (pain reliever); antibiotics, dihydroergotamine (for migraines); chlorhexidine (disinfectant/antiseptic); ACE inhibitors (anti-hypertensive); allergy medicines; chlordiazepoxide & clidinium bromide combination (for treating IBS and ulcer); captopril & hydrochlorothiazide combination (antihypertensive); and dorzolamide & timolol combination (for treating eye conditions).
Medical Problems: Other health problems, which can cause parageusia include: allergies, uremia, dry mouth, candidiasis, depression, stroke, TIA, Bell's palsy, nasal polyps, brain tumor, pemphigus, tooth extraction, Sjogren's syndrome, mastoidectomy, kidney failure, migraine, taste nerve damage, fluid and electrolyte imbalances; chemicals (insecticides), aging process, hypothyroidism, oral neoplasms, diabetes mellitus, smoking, ENT surgery, head trauma/ injury/concussion; poor oral hygiene, hormonal changes (pregnancy, menopause etc.), metabolic and endocrine disorders (thyroid disease, diabetes); mineral and vitamin deficiency; cancer treatment (chemotherapy, radiation therapy); and dental problems (caries, periodontal disease, gingivitis, tooth abscess).
Symptoms of Parageusia
- There are 5 classes of taste which are recognized by the taste buds and these include salty, sweet, bitter, sour and umami.
- The characteristic symptom of parageusia includes alteration in the taste.
- Patient has an increased threshold for sour and sweet tastes.
- Patient also gets confused and is not able to differentiate between bitter and sour tastes; and also bitter and salty taste to some extent.
- Other symptoms, which accompany Parageusia, include lack of desire to eat, nausea, vomiting, anorexia and weight loss.
- Parageusia can be a warning indicating onset of grand mal seizures.
- Parageusia can also be an indication of certain diseases, such as diabetes mellitus, Alzheimer's disease and Parkinson's disease.
- Parageusia and other taste disorders can also cause other health problems, such as eating very less, which results in malnutrition and unhealthy weight loss.
Diagnosis of Parageusia
- Medical history is taken and clinical exam of the patient is done.
- Suprathreshold taste testing of the whole-mouth is done for intensity, quality and pleasantness perception of the 4 taste qualities, i.e. salty, sweet, bitter and sour. The common reagents used for taste testing are citric acid or hydrochloric acid, sucrose, sodium chloride and quinine or caffeine.
- Electrogustometry is electric taste testing which is done to identify taste deficits in specific tongue quadrants.
- Regional gustatory testing can also be done to look for the possibility of loss that is localized to one or more receptor fields.
Treatment of Parageusia
- Treatment of taste disorders, including Parageusia, is limited.
- If the Parageusia is due to infectious causes, such as sinusitis or flu, then it is temporary and treatment of these conditions resolves Parageusia and regains the taste sensation.
- If Parageusia is from drugs then also it can be easily resolved by stopping or changing the offensive medication.
- Parageusia occurring as a result of trauma/injury usually resolves on its own without any treatment.
- If the cause of Parageusia is sensorineural disorders of taste, then there is no effective treatment as such.
- If Parageusia occurs because of stretch injury of chorda tympani nerve in a surgery then it tends to improve over a period of time.
- If there is transection of the chorda tympani nerve, then Parageusia tends to be of permanent nature.
- Idiopathic Parageusia, i.e. Parageusia that has no apparent cause often remains stable or can worsen.
- Complications of Parageusia, if left untreated, include anorexia, malnutrition and weight loss.