Smell Disturbance
Flowchart
Red Flags requiring urgent review
Unilateral nasal obstruction or epistaxis (malignancy)
Headaches or vomiting (intracranial pathology)
Assessment
History
Duration and onset (sudden or gradual?)
Degree of smell loss (total or partial?)
Trigger (onset with URTI, COVID-19, other illness, trauma, known rhinological condition)
Offensive smell (cacosmia, common in chronic rhinosinusitis)
Phantosmia (smell perceived when no smell present, e.g. smoke)
Smells are distorted/everything smells the same (parosmia, common in post-viral loss)
Nasal blockage (bilateral / unilateral / constant / fluctuant)
Epistaxis (bilateral / unilateral / frequency)
Facial pain
Orbital symptoms (ophthalmoplegia, proptosis, pain are red flags)
Headaches or vomiting (intracranial pathology)
Profession
Use of nasal medications
Neurodegenerative symptoms (tremor, bradykinesia, cognitive impairment)
Previous nasal operations
Examination
Nose: polyps or masses, erythematous mucosa (rhinitis), clear secretions, mucopurulent secretions (rhinosinusitis)
Investigations
Rule out abnormalities in thyroid hormone, haemoglobin and haematinics
Differential Diagnosis
Post-viral and idiopathic smell loss
This is probably the commonest cause. There may be an obvious preceding infection (viral URTI, acute rhinosinusitis or COVID-19), or sudden-onset anosmia may occur on its own.
Smell training is effective for many patients, although expectations of full recovery should be managed (www.abscent.org). Trial a nasal steroid spray for 3-6 months and counsel the the patient that steroid will not work immediately. Limited evidence exists for vitamin A nasal drops and omega-3 supplementation.
Acute and chronic rhinosinusitis
Both acute or chronic rhinosinusitis can affect smell. Patients must have nasal blockage and/or rhinorrhoea to be diagnosed with rhinosinusitis - otherwise the cause is most likely post-viral. Initial management is a trial of fluticasone or mometasone nasal steroid spray or drops (for around 3 months, not just one bottle).
If symptoms are well controlled, continue medication longer term. If there is no improvement then consider a referral to ENT.
Head injury
Usually occurs due to shearing damage to the sensory nerves. Recovery of smell can slowly occur up to 2 years post injury. Smell training can have some impact, but less than in post-viral anosmia (www.abscent.org).
Age-related and neurodegenerative
Ageing leads to gradual reduction in sense of smell in the normal population. Smell training can be used. Loss of smell can be associated with Parkinson’s disease and dementia.
Congenital
Patients who have never been able to smell a congenital cause should be considered, e.g. Kallmann’s and Turner’s syndromes.
Toxins
Tobacco, cocaine and some medication (beta blockers, antithyroid medications and ACE inhibitors) can cause smell dysfunction.
Malignancy
Sinonasal or skull-base tumours may lead to anosmia. However, there are almost always significant other symptoms: unilateral nasal obstruction, unilateral epistaxis/blood-stained discharge, orbital symptoms, personality change, headache/raised ICP etc. Make a suspected cancer pathway referral to head and neck or neurosurgery.
Referral pathways
Suspected cancer pathway
Suspicion of sinonasal, skull base or intracranial tumour
Routine referral
Patients with suspected chronic rhinosinusitis not improving with regular intranasal saline and corticosteroid sprays (>3 months)
Diagnostic uncertainty
More information
https://www.nhs.uk/conditions/lost-or-changed-sense-smell/
https://www.fifthsense.org.uk/smell-training/
https://www.ncbi.nlm.nih.gov/books/NBK482152/
https://epos2020.com/Documents/supplement_29.pdf
Authors
Mr Elliot Heward, ENT Registrar, North West Deanery
Mr Thomas Jacques, Consultant Rhinologist/ENT Surgeon, St. George’s Hospital, London