Exodontia.Info
Taste Disturbances
Useful Articles:

Dental Update 1999.  Halitosis and Disturbances of Taste, Orofacial Movement or
Sensation

BDJ 2000.  Persistent impairment of taste with terbinafine

BMJ 2002.  Dysgeusia and burning mouth syndrome by eprosartan

Cleveland Clinic Journal of Medicine 2002.  Management of smell & taste problems

American Dental Association 2005.   Burning Mouth Syndrome

CPJ  2006.  Taste disturbances linked to drug use

Encyclopedia of Neurological Disorders 2007.  Dysgeusia

Oral Diseases 2011.  Taste Dysfunction.  A Practical Guide for Oral Medicine

Cochrane Collaboration 2012.  Interventions for the Management of Taste
Disturbances (Protocol)


Taste Disturbance.  Oral Medicine Clinic, Eastman Dental Institute

Taste Disturbances - 10 Steps Towards Control.  Oral Medicine Clinic, Eastman
Dental Institute
Treatment Algorhithm for Taste Disturbances
Last Updated 27th November 2013
Smell & taste disorders are common in the general
population, with loss of smell occurring more frequently.

The tongue can detect only sweet, salty, sour, bitter &
‘savoury’ (
umami) tastes.  Much of what is perceived as
"taste" is actually “smell”.  People who have taste
problems often have a smell disorder that can make it hard
to identify a food's flavour.  (
Flavour is a combination of
taste and smell [mainly] and texture & temperature).

Problems range from distorted taste (
dysgeusia), reduced
sense of taste (
hypogeusia) to a complete loss of the
sense of taste (
ageusia).  However, a complete inability to
taste is rare.

Taste problems can be caused by anything that interrupts
the transfer of taste sensations to the brain (or
vice versa)
or by conditions that affect the way the brain interprets
these sensations.

Advancing age has been associated with a natural
impairment of smell and taste ability.
Types of Taste Loss

There are several ways of classifying taste disorders but the method most
commonly applied in clinical practice, is to distinguish
qualitative from quantitative
taste disturbance as follows:

Dysgeusia: qualitative taste impairments, which include a multitude of complaints,
such as metallic taste or permanent bitter, sour, salty or (even rarer) sweet taste.

Hypogeusia: a quantitative taste disturbance producing reduced taste function

Ageusia: a quantitative taste disturbance producing absence of taste.

Any of these can be triggered, lowered or unaffected by eating.

According to testing with
taste strips, 5.3% of the people considered as healthy
have
hypogeusia and very few complete ageusia.

Other classifications are based on the anatomical site of the lesion (e.g.
peripheral
nerve
lesion, brainstem lesion, thalamic or fronto-orbital lesion).


Causes

Taste sensation often decreases after age 60.  Most often, salty and sweet tastes
are lost first.  Bitter and sour tastes last slightly longer.


Selected Possible Causes of Taste Disturbance

Common causes


Medications can be responsible for taste loss and should be reviewed in all
patients with
gustatory disturbance.

Xerostomia / excessive dryness of the oral cavity is a common side effect of a
number of medications (e.g.
anti-cholinergics, anti-depressants, anti-histamines)
and disease states (e.g.
Sjögren's syndrome, xerostomia, diabetes mellitus).

Less Common Causes

  • Nutritional factors (e.g. vitamin deficiency [B3, B12], trace metal deficiency
    [zinc, copper], malnutrition, chronic renal failure, liver disease [including
    cirrhosis], cancer, AIDS)
  • Tumour or lesions associated with taste pathways (e.g. oral cavity cancer,
    neoplasm of skull base)
  • Head trauma / Injury to the mouth, nose or head
  • Toxic chemical exposure (e.g. benzene, benzol, butyl acetate, carbon
    disulfide, chlorine, ethyl acetate, formaldehyde, hydrogen selenide, paint
    solvents, sulphuric acid, tri-chloro-ethylene)
  • Industrial agent exposure (e.g. chromium, lead, copper)
  • Radiation treatment of head and neck

Uncommon Causes

  • Psychiatric conditions (e.g. depression, anorexia nervosa, bulimia)
  • Epilepsy (gustatory aura)
  • Migraine headache (gustatory aura)
  • Sjögren's syndrome
  • Multiple sclerosis
  • Endocrine disorders (e.g. adreno-cortical insufficiency, Cushing's syndrome,
    diabetes mellitus, hypo-thyroidism, pan-hypo-pituitarism, pseudo-hypo-
    parathyroidism, Kallmann's syndrome, Turner's syndrome)


Step-by-Step Diagnostic Approach

The evaluation of a patient presenting with taste dysfunction comprises the
patient's history (including drug intake and nutritional elements), a detailed clinical
examination (of the head, neck, ears, nose & mouth), and investigations to
determine the underlying ætiology.


History

It is important to determine whether the patient can discern salt, sweet, bitter, sour
and whether the taste disturbance is
quantitative (hypogeusia / ageusia) or
qualitative (dysgeusia).

It is important to determine whether the taste disturbance was acute in onset or
was gradual.  Acute taste loss is associated with
iatrogenic (medically-related) or
toxic causes whereas a more insidious onset may suggest a neurological (nerve
dysfunction) or
neoplastic (benign or malignant cancer) origin.  Any concomitant
loss of
nasal function (i.e. smell & flavour) should also be ascertained.

A full medical history is taken including what medications / drugs the patient is on.  
Assessment of existing medical conditions (such as
endocrinopathies or
neurological conditions) can put the taste disturbance in context.  A history of any
precipitating event (such as recent trauma, medical procedure or radiotherapy) is
needed as well.


Physical Examination

A thorough examination of the head, neck, mouth & ears should be performed to
look for obstruction, inflammation, previous surgery & infection.

  • A complete examination of the oral cavity (mouth) & naso-pharynx is done
    with particular attention to signs of previous surgery (such as missing 3rd
    molars [wisdom teeth] & tonsils).

    Mucous membranes should be evaluated for dryness, leukoplakia (white
    patches) & exudates.  The patient's teeth and gingivæ (gums) should also be
    examined as severe dental caries (tooth decay), gingivitis (gum disease) &
    intra-oral abscess can result in a malodorous and caustic oral environment
    that disturbs the senses of smell and taste.  Evidence of mucosal inflammation
    suggests possible nutritional deficiencies (such as chronic iron, zinc or B12)
    or inflammatory process.

    Oral candidal infections in immuno-compromised patients (e.g., those who
    have received chemotherapy or who have AIDS) can produce white patches
    or diffuse erythema (redness).  Viral infections (e.g. herpes simplex virus,
    coxsackie virus) tend to cause the development of vesicles (blisters) with
    surrounding erythema, which then evolve into erosions or ulcers.

    A dry mouth (xerostomia) is looked for – signs include angular cheilitis,
    cervical (around the ‘neck’ of the tooth) dental decay, tooth loss & mucous
    threads.


  • The eyes should be checked for any sign of dryness (xerophthalmia) such as
    kerato-conjunctivitis sicca.

  • The neck should be checked for any previous neck surgery or thyroid
    enlargement.

  • The major salivary glands (the parotid & submandibular) should be checked
    for possible enlargement (suggestive of Sjögren’s Syndrome).

  • Depending on the clinical history, a neurological examination may be
    warranted.  This should include a careful evaluation of cranial nerve function.


Chemo-Sensory Gustatory Testing

It is difficult for patients to measure taste disturbances objectively, so chemical
gustometry
/ electro-gustometry should be used.


Chemical Gustometry

Solutions of the 4 fundamental tastes (sweet, sour, sweet & bitter; occasionally,
umami) are applied to the tongue surface.

Results are reported as any decrease of taste sensation on the area of the tongue
tested.


Electro-Gustometry

An electrode is used to breakdown water (hydrolysis) in the saliva.  This stimulates
the taste buds eliciting a sour, sometimes metallic, taste recognised by the patient.

Results are reported as non-detectable or increased thresholds on the areas of the
tongue tested.


Olfactory Testing

In most patients with taste disturbances, olfactory function should be assessed.  
This is more objective if tested than just asking the patient.

There are a number of validated olfactory testing methods (such as the
Smell
Identification Test, the Pocket Smell Test, the Brief Smell Identification Test and
the
Odor Threshold Test); these are all based on similar principles.

Odours are presented to the patient & they have to identify the smelled odour from
4 possibilities.  According to the number of correctly identified odours, the patient is
categorised as
normosmic, hyposmic or anosmic.


Laboratory Investigations

Clinical laboratory tests may be helpful in ruling out co-existing medical conditions
suggested by the history & physical examination, such as infection, nutritional
deficiency, allergy, diabetes mellitus & thyroid, liver or kidney disease (such as
FBC, peripheral blood smear, serum ferritin, vitamins B12 & folate, zinc, thyroid
function tests
, liver function tests, oral glucose tolerance test, serum fasting
morning glucose test
, Ro-La antibodies & acetylcholine receptor antibody [if
myasthenia gravis suspected]).


Imaging

When structural or inflammatory causes of smell or taste loss are suspected,
imaging studies may be helpful in selected patients.  However, all imaging
techniques have limitations & negative tests cannot rule out structural lesions.

Computed tomographic (CT) scanning is the most useful technique for assessing
skull fractures,
intra-cranial bleeds, sub-dural hæmatoma or areas of ischæmia.  
It also picks up well
Alzheimer’s Disease, Multiple Sclerosis, sino-nasal tract
inflammatory
disorders.

The use of
intravenous contrast media helps to better identify vascular lesions,
tumours, abscess cavities &
meningeal or para-meningeal processes.

MRI is superior to CT scanning in the evaluation of soft tissues but it poorly defines
bony structures.  
MRI is the technique of choice for assessing the olfactory bulbs,
olfactory tracts, facial nerve & intra-cranial causes of chemo-sensory
dysfunction
.  It is also the preferred technique for evaluating the skull base for
invasion by
sino-nasal tumours.  Gadolinium enhancement is useful for detecting
dural or lepto-meningeal involvement at the skull base.
Treatments

Many taste disorders (dysgeusias) resolve spontaneously within a few years of
onset.

However, several immediate steps can be taken to help correct a taste
disturbance.  For example, some drug-related
dysgeusias can be reversed with
cessation of the offending drug.

Conditions such as
radiation-induced xerostomia & Bell's Palsy generally improve
over time.  An artificial saliva (e.g.
Xerolube) may be helpful in patients with
xerostomia.

The causes of
olfactory dysfunction that are most amenable to treatment include
obstructing polyps or other masses (treated by excision) and inflammation
(treated with
steroids).


Enhancement of food flavour & appearance can improve quality of life in patients
with irreversible taste disturbance.  Patients should be cautioned not to overindulge
as compensation for the bland taste of food.

For example, patients with
diabetes may need help in avoiding excessive sugar
intake as an inappropriate way of improving food taste.  Patients with taste
disturbance should use measuring devices when cooking, not “cook by taste.”  
Optimising food texture, aroma, temperature and colour may improve the overall
food experience when taste is limited.