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Anosmia

Medicine > Infection

Differential Diagnosis Schema 🧠

Obstructive Causes

  • Nasal polyps: May present with nasal obstruction, reduced sense of smell, and a history of allergic rhinitis.
  • Chronic sinusitis: Often associated with nasal congestion, facial pain, and postnasal drip.
  • Septal deviation: Causes mechanical obstruction, may be associated with a history of trauma or congenital anomalies.

Infectious Causes

  • Viral upper respiratory tract infections (URTI): Common cold, influenza; may present with preceding cold symptoms.
  • COVID-19: Acute onset anosmia, often without nasal congestion, may be accompanied by other systemic symptoms.
  • Chronic rhinosinusitis: Persistent sinus infection, often with associated nasal discharge and facial pain.

Neurological Causes

  • Parkinson’s disease: Progressive neurological disorder; anosmia may be an early sign, preceding motor symptoms.
  • Alzheimer’s disease: Progressive cognitive decline; anosmia may be one of the first symptoms.
  • Head trauma: History of head injury; may present with anosmia due to damage to the olfactory nerve.

Idiopathic Causes

  • Idiopathic anosmia: No identifiable cause after thorough investigation.
  • Congenital anosmia: Present from birth; may be associated with other congenital anomalies.

Key Points in History 🥼

Onset

  • Acute: Suggests infectious causes such as URTI or COVID-19.
  • Gradual: More consistent with neurodegenerative diseases like Parkinson’s or Alzheimer’s disease.
  • Post-traumatic: History of head injury should raise suspicion for traumatic anosmia.

Symptoms Associated

  • Nasal congestion, rhinorrhoea: More suggestive of obstructive or infectious causes.
  • Cognitive decline, motor symptoms: Point towards neurodegenerative conditions.
  • Facial pain, pressure: Indicative of sinus-related causes.

Background

  • Past Medical History: Chronic rhinitis, sinusitis, history of head trauma, or neurodegenerative disorders.
  • Drug History: Certain medications (e.g., antihypertensives, antipsychotics) can cause anosmia.
  • Family History: Genetic predispositions, such as Kallmann syndrome.
  • Social History: Occupational exposures, smoking, or recreational drug use may be relevant.

Possible Investigations 🌡️

Olfactory Testing

  • Smell identification tests: Standardised tests (e.g., UPSIT) to assess the degree of smell loss.
  • Olfactometry: Quantitative assessment of olfactory function.

Imaging

  • MRI of the brain: Useful to excludecentral causes, such as tumours or neurodegenerative diseases.
  • CT scan of the sinuses: To assess for sinusitis, polyps, or other anatomical causes.

Blood Tests

  • Inflammatory markers: ESR, CRP for possible sinusitis.
  • Autoimmune screening: ANA, ENA if autoimmune aetiology is suspected.

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Infection