neurological causes of loss of taste and smell

19 January 2021, Comments: Comments Off

 G Assessment of gustatory function by means of tasting tablets. Arch Neurol.  et al Extraneural organ involvement in human rabies.  N Disturbances of taste and smell induced by drugs. Our website uses cookies to enhance your experience.  GY Central pathway of taste: clinical and MRI study. Many patients do not spontaneously report on their taste disorder, particularly if other symptoms are present.11 Therefore, it is important to specifically ask the patient about any taste-related clinical problems. Small  LM Taste: robust across the age span? (3) Is it caused by damage to the peripheral or central nervous system?  et al Oral mucosal blood flow in patients with burning mouth syndrome.  PGil  T  RF The molecular physiology of taste transduction.  M A double-blind study of the effects of zinc sulfate on taste and smell dysfunction.  SKForssell Smith  AMcCabe Studies suggest it better predicts the disease than other well-known symptoms such as fever and cough, but the underlying mechanisms for loss of smell in patients with COVID-19 have been unclear. Henkin  JGWeber Your nose and an area in the upper throat have special cells that contain odor receptors.  CBancaud LN indicates lingual nerve; PVN, posterior medial ventral nucleus of the thalamus; INS, insula; ?, some fibers cross at the mesencephalon level; CTT, central tegmental tract; ML, medial lemniscus; and NST, nucleus of the solitary tract. For regional testing, 20 to 50 µL of liquid stimuli may be presented to the anterior and posterior tongue using a pipette; other methods are based on the use of soaked filter-paper disks or cotton swabs. In addition, gustatory dysfunction is rare, eg, compared with olfactory disorders.2,3 Therefore, the scope of this review from a neurological viewpoint is to alert physicians to the problem of taste disorders and to help in the diagnosis.  CHeckmann  RBaruzzi  DVSt John For example, high pesticide exposure can cause long-lasting impairment of the sense of smell and taste. identified only 10% of the patients with a taste problem. However, although electrogustometry is widely used, there seems to be a poor correlation between electrically and chemically induced sensations.19, With the finding of gustatory dysfunction, several electrophysiological tests may be applied to identify abnormalities in the nerve to brainstem pathways, which is of importance in cases of trigeminal neuropathy, multiple sclerosis, and pontine lesions. Other tests include identification or discrimination of common taste substances.  AStemper However, a less accurate estimate of taste intensity was observed in patients with excisions from the left or right anteromedial temporal lobe. Customize your JAMA Network experience by selecting one or more topics from the list below.  M Changes in taste intensity perception following anterior temporal lobe removal in humans.  NShoji Gustatory receptor cells are located within taste buds, which are contained in the papillae (approximately 250 buds per circumvallate papilla).  JMMorin All Rights Reserved.  HPhelan A partial or complete loss of taste can be troublesome as we depend on our taste buds to warn us of potential food dangers and control our eating habits.  SCMargolskee Topical anesthesia of the tongue has been reported to be of use in the diagnosis of dysgeusia.3, In addition to techniques based on administration of chemicals to the tongue, electrogustometry is frequently used.18 It is based on the induction of gustatory sensations by means of an anodal electrical direct current.  RJJones-Gotman  DAEslinger Particularly in patients with bilateral lesions, the loss of hedonism may result in impaired appreciation of foods, which, in turn, leads to changes in food intake, followed by clinically significant weight loss.33.  D Automated electrogustometry: a new paradigm for the estimation of taste detection thresholds. Taste cells are known to have regenerative capabilities, with an approximate life span of 10 to 20 days.4 The actual taste organ consists of approximately 10 000 taste buds, which are situated predominantly on the tongue and soft palate, each with 50 to 150 receptor cells.5 Afferent nerves make contact with the receptor cells at the base of the taste bud. Woschnagg  ASBaborie Schiffman The history should also focus on the possibility of accompanying diseases, eg, diabetes mellitus, hypothyroidism, or cancer.13 Clinical examination includes inspection of the tongue and the oral cavity. For example, the blink reflex may be used to evaluate the integrity of the pathway trigeminal nerve–pontine brainstem–facial nerve.20.  B  HJ Butterscotch masks the bitter taste of sumatriptan nasal spray [letter]. Uchiyama In particular, using special sequences, magnetic resonance imaging allows visualization of the CNs.21 Furthermore, it provides significant information in terms of the type and cause of a lesion.  S Reversible ageusia induced by losartan: a case report. Sumner  RF Molecular mechanisms of bitter and sweet taste transduction.  HNeundörfer Heckmann no taste disorder was confirmed in 94%.12 In contrast, the question "Do you have a taste problem?" A single taste bud may be innervated by several afferents, while a single fiber may innervate several taste buds.  BF Temporal lobe tumor manifested by localized dysgeusia. In other disorders of the chemical senses, an odor, a taste, or a flavor may be distorted.  BF Simultaneous involvement of third and sixth cranial nerve in a patient with Lyme disease. Patients usually report sour or metallic sensations similar to those associated with touching a battery with the tongue. Hummel  JNSolomon For some people, normally pleasant tastes or smells may become unpleasant. Once the cold runs its course, a person's sense of smell returns. In the lower left, the main peripheral gustatory pathway is shown (branch of cranial nerves [CN] V and CN VII; the remaining branches of CN IX and X are not shown); on the right, the central gustatory pathways are given.  JMBeis Together, these data suggest that COVID-19-related anosmia may arise from a temporary loss of function of supporting cells in the olfactory epithelium, which indirectly causes changes to olfactory sensory neurons, the authors said. For whole mouth testing, small quantities (2-10 mL) of solution are administered, and the patient swishes them around in the mouth.  SMHeckmann  RF Mechanisms of taste transduction. The tongue is also innervated by the trigeminal nerve, which is involved in tasting through the perception of touch, pressure, temperature, and pain (eg, spicy foods).  PJFriedewald  MGHummel "3,14 In this test, 3 drops of liquid are presented to the subject (one of them being the taste stimulus and 2 being pure water; volume, <0.1 mL).  BCHwang The loss of the senses of smell and taste are the most common smell and taste disorders. However, few studies are found in the medical literature on taste disorders, including authoritative textbooks of neurology and internal medicine.1 One reason for this may be that gustatory functions are tied to the sense of smell, the somatosensory system, and the perception of pain (eg, when spicy food is eaten), which makes it difficult to examine sensations mediated through an individual system. Lack of taste can cause a decrease in appetite, which can lead to unhealthy weight loss.  E Depressed taste and smell in geriatric patients. Adapted from Lee et al10 and Sanchez-Juan and Combarros.1. For example, taste disorders have been reported in familial dysautonomia,1,13 hereditary ataxia,1 Machado-Joseph disease,46 and Guillain-Barré syndrome,1 probably due to dysfunction of small nerve fibers. Head trauma Injury to the head can cause you to lose your sense of smell and taste.  JGHilz Some 86% of people with mild cases of COVID-19 lose their sense of smell and taste but recover it within six months, according to a new study of over 2,500 patients from 18 European hospitals. Typical clinical investigations involve sialometry and sialochemistry.23, Compared with other sensory dysfunctions, an interdisciplinary approach combining dental, neurological, and otorhinolaryngological expertise seems to be especially important to effectively diagnose and treat disorders of the sense of taste.24 Based on teamwork, causes such as sarcoidosis, rheumatoid arthritis, immunological disorders, vitamin B12 deficiency, dental disorders, salivary dysfunction, and infections are easily diagnosed and treated using an interdisciplinary approach.13, Using quantitative measures, taste disorders can be described as ageusia (complete loss of taste), hypogeusia (diminished sense of taste), or hypergeusia (enhanced gustatory sensitivity). All Rights Reserved, Challenges in Clinical Electrocardiography, Clinical Implications of Basic Neuroscience, Health Care Economics, Insurance, Payment, Scientific Discovery and the Future of Medicine, United States Preventive Services Task Force, 2003;60(5):667-671. doi:10.1001/archneur.60.5.667. After synapsing at this level, gustatory fibers project to the corresponding hemisphere, where the insular cortex, frontal operculum, opercular part of the superior temporal gyrus, and inferior part of the precentral and postcentral gyri are crucial projection zones of cortical representations. Taste and smell disorders send hundreds of thousands of Americans to the doctor each year.  TArai Therefore, it may be practical to differentiate 3 types of central taste disorders with lesions at the level of the brainstem, thalamus, or cortex.1. A discrete taste loss in older persons is frequent but rarely causes significant clinical problems.44 Following quantitative gustatory testing and appropriate clinical examinations, patients usually can be counseled such that the problem has no life-threatening cause and that the addition of seasonings to foods, tongue cleansing, or cessation of smoking may be helpful remedies.45, There are numerous conditions presenting with gustatory dysfunction in which exact localization in the nervous system is not possible.  DMZatorre There is now evidence that a receptor cell may respond to a particular taste, but the same cell may also respond to other tastes.7 This means that there is not always a correlation between chemical stimulant and perceived taste quality; in turn, different types of chemicals can evoke similar sensations. Kobal Fahy At its worst, this deficit may become a life-threatening hazard. Although many of the tests are based on ratings using visual analog scales, some of these methods use magnitude-matching procedures.  MRiva  CQuinonez Structural imaging is routinely used to investigate lesions in the taste pathway. Terms of Use|  JSChoi  A Zur Topik des Verlaufes der Geschmackssinnsfasern und anderer afferenter Bahnen im Thalamus. Gustatory dysfunction due to central lesions is, by definition, the result of a disturbance in the taste pathway originating from the level of the brainstem that includes the solitary tract nucleus up to its cortical representation.  RPGoldsmith anosmia, doesn’t just happen with COVID-19. When viral infections and head injury cause taste problems, tincture of time can lead to recovery.  NPaysant  SJ Neural coding of gustatory information.  C Dysgeusia resulting from internal carotid dissection: a limited glossopharyngeal nerve palsy.  T Zinc gluconate in the treatment of dysgeusia: a double-blinded controlled study [abstract].  JGHiIz In addition, the analysis of saliva should be performed, as it constitutes the environment of taste receptors, including transport of tastes to the receptor and protection of the taste receptor. Some of the more common ones include allergies, diseases such as Alzheimer's and Parkinson's, medication side effects, dental issues and cigarette smoking. Stillman What Causes Loss of Taste or Impaired Taste? More recent investigations in patients who have had strokes indicated that dysgeusia was present contralaterally to a thalamic or corona radiata infarction, thus supporting the idea that gustatory fibers ascend contralaterally in the cerebral hemisphere and that the pathway ascends from the thalamus to the cerebral cortex via the posterior part of the corona radiata.1 However, there are reports indicating that an ipsilateral lesion of the thalamus can result in hemihypogeusia,1 thus supporting the theory that crossing of fibers occurs at the lower brainstem level. Data rates may apply. When these receptors detect smells, they … What is smell? Numerous mechanisms of drug-induced gustatory dysfunction have been identified, including deposition of silver sulfate, altered influx of calcium and other ions, chelation or depletion of zinc, disturbed bradykinin catabolism, alteration of second messenger synthesis, and altered prostaglandin metabolism.26 Lists of drugs that may cause taste problems have been compiled by Schiffman13 and by Ackerman and Kasbekar.26 Among others, drugs used to treat epilepsy (carbamazepine, phenytoin sodium, and lamotrigine27), spasticity (baclofen), Parkinson disease (levodopa), pseudotumor cerebri (acetazolamide), migraine (triptans28), diabetes mellitus (glipizide), and arterial hypertension (captopril and losartan potassium29) should be considered as candidates responsible for gustatory dysfunction.  JGTomandl sign up for alerts, and more, to access your subscriptions, sign up for alerts, and more, to download free article PDFs, sign up for alerts, customize your interests, and more, to make a comment, download free article PDFs, sign up for alerts and more, Archives of Neurology & Psychiatry (1919-1959),,, FDA Approval and Regulation of Pharmaceuticals, 1983-2018, Global Burden of Skin Diseases, 1990-2017, Health Care Spending in the US and Other High-Income Countries, Life Expectancy and Mortality Rates in the United States, 1959-2017, Medical Marketing in the United States, 1997-2016, Practices to Foster Physician Presence and Connection With Patients in the Clinical Encounter, US Burden of Cardiovascular Disease, 1990-2016, US Burden of Neurological Disease, 1990-2017, Waste in the US Health Care System: Estimated Costs and Potential for Savings, Register for email alerts with links to free full-text articles.  SWichmann Typically, after a couple of seconds, the solutions are spit out and the patient rinses the mouth with tap water.3, Threshold tests for sucrose (sweet), citric acid (sour), sodium chloride (salty), and quinine or caffeine (bitter) are frequently performed with natural stimuli.3 One of the most frequently used techniques is the "3-drop test. But when in doubt, reach out to your doctor. Many gustatory disorders are induced by drugs. Jaaskelainen Taste Loss and Aging. Gilbertson  PJ Taste perception in patients with insular cortex lesions. Heckmann The chemicals that produce sweet or bitter taste typically bind to surface receptors, triggering a cascade of signals that results in conformational changes in ion channels.8 A key member of this cascade is gustducin.9 Following activation of the taste buds, gustatory information is carried primarily by specific branches of 3 cranial nerves (CNs). Hausser-Hauw  R Role of saliva in the maintenance of taste sensitivity.  MAl-Din  et al Smell and taste disorders: a study of 750 patients from the University of Pennsylvania Smell and Taste Center. For example, local causes need appropriate dental, dermatological, or otorhinolaryngological care; underlying schizophrenia or depression requires psychiatric treatment.  T Machado-Joseph disease associated with an absence of fungiform papillae on the tongue. New research is showing a connection between a loss of smell and taste and the coronavirus. True taste loss, however, is rare.  A New variant Creutzfeldt-Jakob disease presenting with loss of taste and smell. Cultures are indicated when fungal or bacterial infections are suspected. Frequently, gustatory stimuli are reported to be different from what they used to be; they are perceived as bitter, sour, or metallic. A nasty cold, the flu, even bad allergies can cause nasal congestion that renders those senses useless. Key points about smell and taste disorders.  FA Taste and smell problems: validation of questions for the clinical history. Text.  SRenner Most often, people are experiencing a loss of smell instead of a loss of taste. By experiencing anosmia, you can expect a change in the way things taste as well.  BMaihöfner  CNordin  TADeSilva  A Dysgeusia in epileptic patients treated with lamotrigine: report of three cases.  SGarg Smell or taste hallucinations . Disorders of taste and smell play a very important role in many neurological conditions such as; head trauma, facial and trigeminal nerve impairment, and many neurodegenerative disorders such as Alzheimer’s, Parkinson Disorders, Lewy ody Disease and Frontal Temporal Dementia.  O Abnormalities of the blink reflex in burning mouth syndrome.  HP Peripheral facial palsy: etiology, diagnosis and treatment.  KNakagawa  AChakrabarty In patients treated surgically for hippocampal sclerosis, gustatory auras persisted in many cases.1 In drug-resistant temporal lobe epilepsy, seizures in all investigated cases were found to invade the insular cortex; a few seizures originated in the insula itself.  J Gustatory hallucinations in epileptic seizures: electrophysiological, clinical and anatomical correlates. No longer able to enjoy food, patients with anosmia may no longer eat enough, or skip meals altogether.  RL Renewal of cells within taste buds.  et al Quantitative assessment of gustatory function in a clinical context using impregnated "taste strips" made from filter paper. Loss of taste and smell also might tempt you to use excess salt or sugar on your food to enhance the taste — which could be a problem if you have high blood pressure or diabetes. Analysis of mucosal blood flow in the oral cavity in combination with the assessment of autonomous cardiovascular factors appears to be useful in the diagnosis of autonomic disorders in burning mouth syndrome16,22 and in patients with inborn autonomic disorder,1 both of which are associated with gustatory dysfunction. Adler  B Collet-Sicard syndrome due to coiling and dissection of the internal carotid artery.  MSchmid  CC  RBZagraniski Taste disorders due to high altitude sickness are hypothesized to be related to hypoxic damage of nerve fibers.1 Taste disorders are also observed in craniofacial trauma, albeit much less frequently than olfactory disorders.11 Recently, hypogeusia has been described as a prominent early feature of the new variant of Creutzfeldt-Jakob disease, probably caused by deposits of prions in the central gustatory pathway.47 Finally, in human rabies virus, antigen was demonstrated in the plexuses of the salivary glands.  DLRaff Loss of smell, a.k.a. They ascend farther to the thalamus, where the ventral posteromedial nucleus is the synapsing region (Figure 1).  R Taste impairment in Alzheimer's disease. Keep in mind that the loss of taste and smell from Coburn 19 is significantly different. Although the perception of a flavor, eg, cherry, is complex and integrates gustatory, olfactory, and somatosensory perceptions, for didactic reasons, we will focus in this review on gustatory disorders from a neurological viewpoint. Ohkoshi  ACYe  O Gustatory nervous pathway syndromes [in Spanish]. Bartoshuk  TKnecht Taste sensations are described as sweet, sour, bitter, and salty.  KHattori And it is said that the cause of it is the coronavirus infecting the cells around the nerves for smell and taste. Lell In idiopathic CN VII palsy (Bell palsy), gustatory dysfunction can be the predominant and sometimes earliest symptom.30 Other causes of CN lesions should be considered, eg, neuritis due to neuroborreliosis or herpes zoster, space-occupying processes in the cerebellopontine angle such as meningioma or neurinoma, or neoplastic processes affecting the submandibular region or the skull base.13,30 A more frequent cause of CN lesions is dissection of the cervical arteries.31 In this situation, the caudal CN can be affected itself or with other nerves.32 Rare causes of the peripheral gustatory system include iatrogenic lesions (eg, following laryngoscopic manipulations33), neuralgia, and polyneuropathies (eg, due to diphtheria, porphyria, lupus, or amyloidosis1,13). The sense of taste is generally regarded as less important compared with vision and hearing. Why does COVID-19 cause a lost sense of taste or smell? All Rights Reserved. It has been shown to be useful in the identification of gustatory deficits in patients with burning mouth syndrome.16, Suprathreshold tests are used to assess the patient's ability to differentiate between different intensities and to estimate the magnitude of suprathreshold loss. Because sense of smell is required for sense of taste, when patients become anosmic they often lose their sense of taste as well. Frequent causes are demyelinating processes or ischemia and hemorrhage; vascular and traumatic lesion sources should be considered.1,10 Lesions in the mesencephalon rarely lead to hypogeusia or ageusia. In: Calhoun Margolskee This approach also includes a thorough review of drugs taken by the patient. Heckmann Temporary loss of smell, or anosmia, is the main neurological symptom and one of the earliest and most commonly reported indicators of COVID-19.  JFGoodspeed The main causes of taste disorders are head trauma, infections of upper respiratory tract, exposure to toxic substances, iatrogenic causes, medicines, and glossodynia (" burning mouth syndrome (BMS)").  D Disturbance of the senses of smell and taste after head injuries. Smell and taste are processed through the brain, so it might not be surprising that conditions affecting the brain, like Parkinson’s disease or Alzheimer’s disease, are linked to disruptions or a loss of these senses, especially smell.  HP Clinical outcomes of three Parkinson's disease patients treated with mandibular implant overdentures.  SS Taste and smell in disease (first of two parts). Loss of sense of smell, known as anosmia, and taste, known as ageusia, can stem from three main causes: obstruction of the nose, damage to the nose lining, or damage to the olfactory nerve or parts of the brain that deal with smell and taste 2. Because so many diseases can have taste and smell dysfunction as symptoms of the disease process itself it is necessary to evaluate your blood, red blood cells and urine for a variety of parameters to determine if some common or obscure disease process is initiating your taste and smell symptoms. Food poisoning. Loss of smell or taste due to COVID-19 appears to last slightly longer compared to other upper respiratory infections. Gent  TFukutake © 2021 American Medical Association.  FLiguori The search for the cause of taste dysfunction should bear in mind the following considerations: (1) Is it caused by drugs? Crossing of gustatory fibers may occur at the lower midbrain level.1 Analogous to the olfactory pathway, taste information also connects to the amygdala and hippocampus. A blockage in the nasal passages caused by a polyp or a nasal fracture also is a common cause. After entering the ipsilateral medulla oblongata and synapsing the nucleus tractus solitarii, the gustatory pathway ascends in the central tegmental tract (not, as previously thought, in the medial lemniscus) to the mesencephalon. Dysgeusia [dis-GYOO-zee-a] is a condition in which a foul, salty, rancid, or metallic taste sensation persists in the mouth. This emphasizes the importance of the anterior temporal lobe in gustatory perception; furthermore, in terms of recognition of bitter taste, the right temporal lobe was superior to the left one.35 Apart from epilepsy, other causes, mainly cerebrovascular and neoplastic, should be considered.36-39 It is unclear the extent to which gustatory dysfunction related to migraine,40 schizophrenia, major depression,1 dementia,41,42 or eating disorders43 is based on cortical dysfunction. In: Vinken The loss of smell (or taste) is one of many emerging hints that the SARS-CoV-2 virus may affect the nervous system. If you're experiencing loss of taste and smell, consult your doctor. Privacy Policy| Get free access to newly published articles. Neurological entities causing taste disorders, Neurological causes with undetermined localization.  RG  FHartung  RChang Complications of Loss of Taste or Smell After Head Trauma. In addition, gustatory-evoked potentials17 may be useful in the diagnosis of taste loss, especially in medicolegal cases. Accessibility Statement. Thalamic taste disorders have been recognized since 1934, when Adler34 described a patient with right-sided hemihypesthesia of the face and right-sided hypogeusia due to an idiopathically diagnosed glioblastoma that infiltrated the left nucleus ventralis posteromedially.  BPierrot-Deseilligny It can even pose an existential threat, by putting … Loss of taste and smell can have a severe impact on daily life in ways most people do not realize.  S Altered food preference after cortical infarction: Korean style. Corresponding author and reprints: Josef G. Heckmann, MD, Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, 91054 Erlangen, Germany (e-mail: (2) Is it caused by local factors, eg, atrophy, injury, or alteration of saliva composition? The sense of taste is based on the detection of chemicals by specialized taste cells in the mouth. © 2021 American Medical Association.  SHRison  RISchecter  CMWarwick  BHKasbekar 2003;60(5):667–671. In addition, tests are being developed that are based on impregnated filter-paper strips.15 This test has a long shelf life, can be used for testing each site separately, and is used with a range of different concentrations of 4 tastes. This is why in some situations it is the sense of smell that is at cause rather than a loss of taste. Ratings of pleasantness may be of value in the diagnosis of dysgeusia.  PCombarros Brainstem taste disorders appear as ipsilateral hemiageusia or hemihypogeusia due to lesions of the bulbar tegmentum at the level of the solitary tract or due to a pontine lesion. From the Departments of Neurology (Drs J. G. Heckmann and Lang) and Prosthodontics (Dr S. M. Heckmann), University of Erlangen-Nuremberg, Erlangen, and the Smell and Taste Clinic and Department of Otorhinolaryngology, University of Dresden Medical School, Dresden (Dr Hummel), Germany.  WTDemets  SSClark Matsuo The loss of smell or taste has emerged as a common early symptom in patients with mild cases of COVID-19. At this level, some fibers cross to the contralateral side. An isolated taste disorder due to a central nervous system lesion is rare.  PSilverstone Covid-19 isn't the first illness to lead to a loss of taste or smell. There are more allergens in your home than you realize, which can cause cove it like symptoms like sore throat, headaches and even a mild loss of taste and smell.  PRussell But other issues can hamper an older person's ability to taste, too. In conclusion, a diagnostic armamentarium is available to determine the cause and severity of gustatory dysfunction. One possibility is that people with upper respiratory infections often have congestion, drainage and other nasal symptoms that can block odor’s ability to reach the smell nerve, which sits at the top of the nasal cavity. Lee In pharmacoresistent epilepsy, approximately 4% of patients report gustatory auras, probably due to focal abnormalities in the opercular parietal region.25 These auras are mainly bilateral. Kinnamon Ahne  TKobal A stuffy nose from a cold is a common cause for a partial, temporary loss of smell. Physicians around the world have documented neurological symptoms in a significant fraction of Covid-19 patients. Accepted for publication December 5, 2002.  S Reliability and validity of electrogustometry and its application to young and elderly persons.

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