What are the differential diagnoses for a man experiencing a sensation of smelling smoke?

Differential Diagnoses for Smelling Smoke in Men

The sensation of smelling smoke when none is present (phantosmia) requires immediate evaluation for temporal lobe pathology, as this is the most critical diagnosis to exclude before considering other etiologies. 1

Most Critical Diagnosis to Exclude

Temporal lobe dysfunction is the most concerning differential diagnosis and must be ruled out first, as it can represent life-threatening pathology including: 1

• Temporal lobe seizures (epileptiform activity) 1, 2
• Brain tumors affecting the temporal or frontal lobes, including meningiomas and esthesioneuroblastomas 3, 2
• Neurodegenerative disease, particularly Lewy body dementia, which can present with phantosmia as an early harbinger before typical hallucinations develop 4

Neurological and Neurodegenerative Causes

Beyond temporal lobe pathology, consider:

• Parkinson's disease - strongly associated with olfactory dysfunction and can present with phantosmia 3
• Alzheimer's disease - olfactory dysfunction serves as an early diagnostic marker 3
• Head trauma - particularly frontobasal trauma causing neural damage to olfactory pathways 3
• Stroke or intracranial hemorrhage - rare but documented causes 5

Post-Infectious Etiologies

• Post-viral olfactory dysfunction following upper respiratory infections, including COVID-19, influenza, and other coronaviruses 3, 5
• Post-infectious phantosmia typically presents with hyposmia first, then progresses to qualitative distortions 1, 5
• Note: COVID-19 affects 59-86% of infected patients with smell/taste loss, presenting as initial symptom in 11.9-22% 3

Sinonasal and Structural Disorders

• Chronic rhinosinusitis with nasal polyposis causing conduction loss from obstruction 3
• Inflammatory lesions including sarcoidosis and granulomatosis with polyangiitis 3
• Tumors affecting the cribriform plate, including squamous cell carcinomas and esthesioneuroblastomas 3

Psychiatric and Mood Disorders

• Depression - associated with olfactory dysfunction, though organic causes must be excluded first 3
• Schizophrenia - can present with phantosmia, but typically lacks insight into the unreality of the perception 5
• Psychiatric disorders should only be considered after neuroimaging excludes structural lesions 1, 2

Medication-Induced Causes

Do not overlook medication-induced phantosmia from: 1

• Anticholinergics
• Corticosteroids
• Dopaminergic agents

Toxic and Environmental Exposures

• Exposure to volatile toxic chemicals in occupational settings (chemical factory workers) 6
• Inhalant misuse (hydrocarbon inhalation) - though this typically presents with acute toxicity rather than isolated phantosmia 7

Nutritional Deficiencies

• Vitamin B12 deficiency - can cause neurological symptoms including sensory disturbances 2
• Iron and zinc deficiency - particularly relevant in patients with restrictive diets 2

Critical Pitfalls to Avoid

Never assume a psychiatric origin without excluding organic causes first - medical and neurological etiologies are common and must be ruled out with appropriate neuroimaging. 1

Do not overlook medication-induced causes - review all current medications including anticholinergics, steroids, and dopaminergic agents. 1

Avoid reflexive prescription of antipsychotics - these are only appropriate when insight is lost or severe psychiatric comorbidity is present. 1

Initial Workup Algorithm

1. Thorough neurological examination focusing on focal deficits, cranial nerve function, and mental status 1
2. Nasal examination to rule out sinonasal pathology 1
3. History of recent infections (URI, COVID-19 exposure) 1
4. Medication review for potential causative agents 1
5. Assessment for associated symptoms: headache, seizure activity, psychiatric symptoms, or other neurological deficits 2

Imaging Recommendations

MRI brain without and with IV contrast is the imaging modality of choice when temporal lobe dysfunction is suspected, using T1-weighted, T2-weighted, FLAIR sequences covering the olfactory epithelium, olfactory bulbs at the cribriform plate, and olfactory pathways in the temporal and frontal lobes. 1, 2

MRI is usually appropriate when red flags are present, including: 1

• New onset hallucinations
• Focal neurological signs
• Lack of insight into unreality of perception