What is the diagnosis and treatment for a patient experiencing olfactory hallucinations of smelling smoke when none is present?

Olfactory Hallucinations (Phantosmia): Diagnosis and Management

Primary Diagnosis: Rule Out Temporal Lobe Dysfunction First

Olfactory hallucinations of smoke require immediate evaluation for temporal lobe pathology, as this is the most critical diagnosis to exclude before considering other etiologies. 1

Key Diagnostic Considerations

The differential diagnosis for smelling smoke when none is present includes:

• Temporal lobe dysfunction (seizures, tumors, degenerative disease) - most concerning 1
• Migraine-associated phantosmia - common in women, typically 5-60 minutes duration 2
• Post-infectious olfactory dysfunction (including COVID-19) - usually presents with hyposmia first 1
• Psychiatric disorders - may lack insight into unreality of perception 1
• Medication-induced - anticholinergics, steroids, dopaminergic agents 3

Initial Workup Algorithm

History Elements to Elicit

• Timing and duration: Brief episodes (5-60 minutes) suggest migraine; continuous suggests other pathology 2
• Associated symptoms: Headache, seizure activity, visual changes, or neurological deficits 1
• Insight preservation: Does patient recognize smell is not real? Lack of insight suggests psychiatric or neurological disease 3, 4
• Unilateral vs bilateral: Unirhinal phantosmia with cyclic pattern suggests focal neurological process 5
• Triggers: Laughing, coughing, Valsalva maneuvers suggest cyclic unirhinal phantosmia 5
• Recent infections: Upper respiratory infection or COVID-19 exposure 1
• Medication review: Complete list including recent additions 3, 6

Physical Examination Priorities

• Thorough neurological examination: Focus on focal deficits, cranial nerve function, mental status 1, 6
• Nasal examination: Rule out sinonasal pathology 1
• Vital signs: Exclude acute medical conditions, infections, delirium 6

Imaging Recommendations

MRI head without and with IV contrast is the imaging modality of choice for evaluating olfactory hallucinations when temporal lobe dysfunction is suspected. 1

Imaging Indications

• Usually appropriate (Rating 8/9): MRI head with and without contrast when red flags present 1
• Red flags requiring imaging: New onset hallucinations, focal neurological signs, lack of insight, seizure activity, progressive symptoms 1, 3
• May defer imaging: Clear temporal relationship to viral infection with confirmed COVID-19 status and no other concerning features 1

What NOT to Order

• CT head is not appropriate for primary evaluation of olfactory nerve dysfunction 1
• CT maxillofacial only useful if sinonasal inflammatory disease suspected, not for hallucinations 1

Treatment Approach

When Temporal Lobe Pathology Excluded

For migraine-associated phantosmia, initiate prophylactic headache therapy as phantosmias diminish or disappear in the majority of patients with this treatment. 2

For Post-Infectious Olfactory Dysfunction

• Olfactory training should be recommended due to simplicity and safety, though evidence is limited 1
• Avoid oral corticosteroids in acute COVID-19 context due to potential viral shedding concerns 1
• Smoking cessation should be recommended for overall benefit 1

For Cyclic Unirhinal Phantosmia

• GABA-activating medications can inhibit phantosmia in both cyclic unirhinal and birhinal forms 5
• Patient-initiated maneuvers: Valsalva, sleep, or nasal water inhalation may provide relief 5

For Severe Distress

• Pharmacological treatment is NOT first-line and reserved only for severe distress despite education 3
• Screen for depression and anxiety at follow-up, as hallucinations may negatively affect functioning 7

Critical Pitfalls to Avoid

• Do not assume psychiatric origin without excluding organic causes - medical and neurological etiologies are common and must be ruled out first 6, 8
• Do not dismiss new-onset or changing hallucinations - these require evaluation for treatable organic factors 8
• Do not overlook medication-induced causes - review all medications including anticholinergics, steroids, dopaminergic agents 3
• Do not prescribe antipsychotics reflexively - only appropriate when insight is lost or severe psychiatric comorbidity present 3

Referral Criteria

• Immediate neurology referral: Focal neurological signs, seizure activity, or abnormal EEG findings 5
• Mental health referral within 30 days: Minimal improvement with initial interventions, severe distress, or loss of insight 6
• Immediate psychiatric referral: Threats of self-harm or harm to others 6