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Disturbances of Taste

Essentials

  • The five primary tastes are sweet, sour, salty, bitter and umami (taste of glutamate).
  • Establish whether what is perceived as a taste defect is not in fact a defect in the sense of smell Disturbances of the Sense of Smell.
    • It may be difficult to differentiate between the perceptions of smell and taste since some of the taste perceptions are perceived as smells that have travelled to the olfactory epithelium via the nasopharynx.
    • While taking history, the patient should be asked about the basic tastes: is he/she able to sense sweet, sour, salty and bitter tastes?
  • Salivary secretion is a prerequisite for the ability to taste.

Decreased ability to taste (hypogeusia)

  • Hypogeusia can result from damage at any level along the gustatory pathway.
    • Damage to the taste buds or the mucous membranes of the oral cavity and pharynx.
    • Injury of the peripheral (cranial) nerves (VII, IX, X)
    • Central causes
  • The chemical reactions necessary for the perception of taste may be disturbed by many different medicinal products and systemic illnesses.
  • Disturbance of taste may be quantitative (ageusia = total inability to taste, hypogeusia = reduced ability to taste) or qualitative (dysgeusia = distorted ability to taste, parageusia = everything tastes bad).
  • Total inability to taste is very rare.
  • Reduced or distorted ability to taste are more common. The distorted sensation often appears as bitter, sour or metallic taste.
  • The disturbance may be associated with aging, neurological disorders, poor oral hygiene, medications, cytostatic chemotherapy, radiotherapy or surgery to the oropharyngeal region.
  • Gustatory hallucinations (phantogeusia) may occur in patients with epilepsy or psychiatric conditions.

Causes of taste disturbance

  • Damage to the mucous membranes of the oral cavity
  • Deficiency of vitamin B12 (the elderly, vegetarians) Megaloblastic Anaemia
  • Medicines
    • Antihypertensive and heart medications: ACE inhibitors, diuretics, calcium-channel blockers, beta blockers, losartan, spironolactone, antihyperlipidaemic drugs
    • Psychoactive drugs: benzodiazepines, tricyclic antidepressants, lithium (metal taste), antipsychotics, hypnotics, CNS stimulants
    • Antibacterials: ciprofloxacin, azithromycin, metronidazole, tetracycline
    • Antifungals: griseofulvin, terbinafine
    • Antivirals: aciclovir, ganciclovir, oseltamivir
    • Neurological drugs: medications for epilepsy, migraine and Parkinson's disease, anticholinergics, acetazolamide, baclofen, dantrolene
    • Cancer drugs
    • Anti-inflammatory drugs: parenteral gold, penicillamine, dexamethasone, beclomethasone, budesonide
    • Metformin
    • Carbimazole
    • Note! Medicine-induced taste disturbances may persist long after the medicine has been discontinued.
  • Lead or mercury poisoning
  • Endocrine diseases (diabetes, thyroid diseases)
  • Systemic renal or liver diseases
  • Autoimmune diseases: Sjögren's syndrome
  • Peripheral nerve damage: facial, glossopharyngeal or vagus nerve damage
    • Nerve damage may be caused by surgery of the head and neck (middle ear surgery, tonsillectomy, hypopharyngeal procedures or dental surgery, for example).
  • Central causes
    • Brain tumour, brain injury
    • Vascular (brain infarction, cerebral haemorrhage)
    • Neurodegenerative diseases (Alzheimer's or Parkinson's disease)
    • Multiple sclerosis

Investigations and treatment

Investigations

  • Careful history taking (whether the disturbance of taste appear instantaneously or gradually, whether any new symptoms have emerged, underlying conditions, drugs and time of their initiation, is it more a disturbance of smell or of taste)
  • Ask about the recognition of basic tastes.
  • A thorough otorhinolaryngological examination
  • Cranial nerve examination (at least for nerves VII, IX and X)
  • In many patients what is perceived as a taste defect is in fact a defect in the sense of smell Disturbances of the Sense of Smell and hence factors that can affect the sense of smell must be excluded (acute rhinitis or preceding upper respitatory infection, maxillary sinusitis, allergic cold, polyposis, injury to the head).
    • Upper respiratory viral infections impair the sense of taste through damage to the sense of smell. During the COVID-19 pandemic, this has happened to many infected with the new coronavirus (SARS-CoV-2) - in some patients the changes in the senses of smell and taste may even be the first symptoms.
  • In specialist care, taste identification tests can be carried out as screening tests to measure quantitative disturbances. There are no tests to measure qualitative disturbances.

Treatment

  • No specific treatment is available to treat disturbances of taste if no clear cause is found for the disturbance in the investigations. Often, however, the sense of taste is restored over time.
  • Good oral hygiene and ensuring the moistness of the mucous membranes is important.
  • Possible fungal infections in the mouth and pharynx must be treated, and the same applies to possible vitamin B12 deficiency.
  • Any medication capable of altering taste should be identified and changed if possible.
  • In disturbances of taste following surgery, the sense of taste is usually restored within months, sometimes even after years.
  • It is worth considering adding spices and flavours to the food and increasing the pleasure of eating, e.g. by improving the presentation.

    References

    • Vennemann MM, Hummel T, Berger K. The association between smoking and smell and taste impairment in the general population. J Neurol 2008 Aug;255(8):1121-6. [PubMed]
    • Doty RL, Bromley SM. Effects of drugs on olfaction and taste. Otolaryngol Clin North Am 2004 Dec;37(6):1229-54. [PubMed]
    • Gamper EM, Zabernigg A, Wintner LM et al. Coming to your senses: detecting taste and smell alterations in chemotherapy patients. A systematic review. J Pain Symptom Manage 2012;44(6):880-95. [PubMed]
    • Welge-Luessen A, Hummel T. Management of smell and taste disorders. A practical guide for clinicians (Ed.1). Thieme Publishers 2014.
    • Sedaghat AR, Gengler I, Speth MM. Olfactory Dysfunction: A Highly Prevalent Symptom of COVID-19 With Public Health Significance. Otolaryngol Head Neck Surg 2020;():194599820926464. [PubMed]
    • Whitcroft KL, Hummel T. Olfactory Dysfunction in COVID-19: Diagnosis and Management. JAMA 2020;():. [PubMed]