Anosmia History
Author – Karthikeyan Sivaganesh Editor – Dr James Mackintosh
Last updated 08/07/24
Introduction
Anosmia is the inability to detect smell and often causes a change in taste perception, hence patients present with both. The olfactory nerve (CN1) supplies smell sensation which enters the nasal canal through the cribriform plate (part of the ethmoid bone). The smell signals are processed by the limbic system and olfactory cortex (found in the frontal lobe). Anosmia can be categorised as conductive (obstructive) or sensorineural (neuronal damage). Note that the sense of smell diminishes with age as olfactory neurons die.
Anosmia common causes
You can split common causes of anosmia into conductive and sensorineural as below:
| Conductive | Sensorineural |
|---|---|
Infection e.g. rhinosinusitis, sinusitis | Viral infection e.g. COVID-19 |
Allergy e.g. allergic rhinitis | Head injury, stroke |
Anatomical e.g. nasal polyps, septal deviation | Medication e.g. ACE inhibitors, diuretics |
Intranasal tumours, nasal cancer | Alcohol, recreational drug use e.g. cocaine |
Vasculitis e.g. granulomatosis with polyangiitis (GPA), eosinophilic GPA | Congenital e.g. Kallmann’s syndrome |
Iatrogenic e.g. sinus surgery (*can also be sensorineural if nerve damage occurs e.g. rhinoplasty) | Neurodegeneration e.g. Parkinson’s disease, Alzheimer’s, multiple sclerosis |
Brain tumours specifically in the frontal lobe |
Presenting Complaint
Site
- Unilateral → nasal polyp, septal deviation, intranasal tumour
- Bilateral (common) → infection, inflammation e.g. vasculitis, malignancy, drug-induced
Onset
- Days → infection, allergy (consider season or weather in history)
- Weeks/months → brain injury, malignancy, COVID-19
- Years → neurodegeneration e.g. Parkinson’s disease, malignancy, illicit drug abuse
Character
- Faint sensation of strong odour (hyposmia) → conductive causes more likely
- No sensation of odour (anosmia) → sensorineural causes more likely
- Progressive loss of smell → intranasal tumours or related malignancy
Associated Symptoms
- Fever, feeling ill, coryza → upper respiratory tract infection (URTI) including COVID-19
- Nasal discharge (rhinorrhoea):
- Mucous → URTI, sinusitis, etc
- Cerebrospinal fluid → basal skull fracture, space-occupying lesions
- Nasal deformity:
- Septum perforation → cocaine inhalation
- Saddle nose deformity → GPA
- Frontal headache → sinusitis (if fever present, consider infective sinusitis)
- Asthma features → allergic rhinitis, eGPA
- If symptoms worse during spring/summer → allergic rhinitis is more likely
- Subfertility/infertility, delayed/absent puberty → Kallman’s syndrome
Red Flags
You should ask about these symptoms as they indicate potentially serious causes of anosmia and may require urgent treatment and/or referral.
- Unilateral nasal symptoms e.g. polyps → nasopharyngeal carcinoma
- Bleeding → nasal tumour
- Crusting within nasal cavity → nasal cancer
- Signs of raised intracranial pressure e.g. headache worse on coughing → brain tumour
- Progressive worsening headache, change in personality → brain tumour
Background
In any history you will ask about past medical history, medications, allergies, social history, and family history. In a history about anosmia, you can show how much you know about the various causes by explicitly asking about the following things:
Past medical history
- Head trauma → brain injury e.g. damage to olfactory neuron pathway
- Nose or sinus surgery → iatrogenic
- Malignancy e.g. prostate cancer, breast cancer → brain metastases
- Hypertension, heart failure → medication-induced anosmia
Social history
- Recreational drug use e.g cocaine → olfactory nerve damage
- Alcohol abuse
Common Differentials in OSCE's
| Condition | Presentation |
|---|---|
COVID-19 | Flu-like/URTI symptoms e.g. headache, runny nose, cough, tiredness. Bilateral anosmia often occurs with changes in taste. |
Brain injury | Typically blunt trauma causing haematoma or skull fracture specifically (basal skull fracture). Consider in elderly patient presenting with confusion or falls. |
Drug abuse e.g. cocaine | Chronic inhalation use (e.g. years), nose deformity specifically nasal septum perforation, heart attack at a young age <40 years |
Neurodegeneration e.g. Parkinson’s, Alzheimer’s | Elderly, signs of parkinsonism (bradykinesia, rigidity, resting tremor), memory problems, progressive nature |
Examination
When examining anosmia, remember common causes. An ear, nose and throat examination focusing on the nose is needed to identify any conductive causes of anosmia and a neurological exam for potential sensorineural causes. Remember common is common! If unsure, be honest and tell the examiner of your findings and how you confirm the possible aetiology e.g. MRI head, endoscopy, etc.
Key points
- Consider the patient’s age
- Look for any visible nose deformity or facial scars
- Use a nasal speculum to identify any polyps
- If examination appears normal, consider further investigations such as imaging, bloods, etc
References/further reading
1. GP Notebook – https://gpnotebook.com/en-GB/pages/respiratory-and-chest-medicine/anosmia [Accessed 12/5/24] 2. GP Notebook – https://gpnotebook.com/en-GB/pages/ear-nose-and-throat/assessment-of-anosmia-in-primary-care [Accessed 12/5/24]