What is the differential diagnosis and appropriate work‑up and treatment for unilateral left naris (nostril) numbness?

Unilateral Left Naris Numbness

Unilateral nasal numbness most likely represents external nasal nerve neuralgia or neuropathy, which requires evaluation to exclude structural lesions, followed by targeted neuropathic pain management if no underlying pathology is identified.

Differential Diagnosis

The key distinction is whether this represents a peripheral nerve problem versus a structural lesion requiring urgent intervention:

Primary Considerations

• External nasal nerve neuralgia/neuropathy is the most common cause of isolated unilateral nasal numbness, presenting as numbness, tingling, or pain strictly limited to the territory of the external nasal nerve (ala nasi and apex nasi) 1, 2
• Post-traumatic neuropathy from direct nasal trauma, even remote injury, can cause persistent numbness due to injury to the external nasal nerve, which exits 6.5-8.5 mm lateral to the nasal midline between the nasal bone and upper lateral cartilage 2, 3
• Idiopathic external nasal neuralgia occurs without identifiable trauma and appears to have a central etiology given poor response to local anesthetics 2

Red Flag Diagnoses Requiring Urgent Evaluation

• Unilateral sinonasal pathology including benign neoplasms (odds ratio 7.8) and malignancy (odds ratio 8.0) are significantly more common with unilateral versus bilateral disease 4
• Invasive fungal disease in immunocompromised patients (diabetes, hematologic malignancies) requires immediate biopsy with mortality rates of 50-80% without urgent intervention 5
• Granulomatous disease (Wegener granulomatosis, sarcoidosis) can present with unilateral nasal symptoms and sensory changes 5

Diagnostic Workup

History and Physical Examination

Look specifically for:

• Trauma history: Any prior nasal trauma, even remote, or recent rhinoplasty 2, 3
• Pain characteristics: Episodic tingling lasting up to 30 minutes, 2-3 times daily versus constant bruised sensation 2
• Associated symptoms: Epistaxis, unilateral rhinorrhea, unilateral nasal blockage, severe headache, or anosmia suggest alternative diagnoses like CSF rhinorrhea, sinonasal tumors, or chronic rhinosinusitis 6
• Immunocompromised status: Diabetes, hematologic malignancies, or immunosuppression raises concern for invasive fungal disease 5

Physical Examination Findings

• Nasal endoscopy to identify red flags: unilateral obstruction with bleeding, crusting, non-healing characteristics, retrotympanic masses, or endoscopic appearance suggesting neoplasia (brick red or black necrotic areas, firm lobulated masses) 5
• Sensory testing of the external nasal nerve distribution (ala nasi and apex nasi) 1
• Examination for unilateral polyps or masses, which mandate tissue biopsy since unilateral disease has a 4.5% diagnostic discrepancy rate versus 1.1% for bilateral disease 5

Imaging Studies

• CT paranasal sinuses is indicated for unilateral nasal symptoms to evaluate for structural lesions, bone destruction, or extrasinus extension before any biopsy 5, 4
• MRI brain and sinuses should be obtained if CT shows concerning findings or if neurological symptoms are present, as neurological conditions like brainstem infarction or cerebellopontine angle tumors can cause unilateral sensory changes 6, 5
• Routine imaging is typically negative in idiopathic external nasal neuralgia, though rare cases may show nasal contact points 2

Laboratory and Additional Testing

• Erythrocyte sedimentation rate is typically negative in external nasal neuralgia but helps exclude inflammatory conditions 2
• Diagnostic nerve block of the external nasal nerve with local anesthetic can confirm the diagnosis if it achieves marked reduction in symptoms 1, 2

Treatment Approach

When Structural Pathology is Excluded

• Pregabalin shows good results as preventive treatment for external nasal neuralgia 2
• Tricyclic antidepressants, specifically amitriptyline, though very few patients respond to this option 2
• External nasal nerve blockade with local anesthetic provides effective treatment, with most patients responding to this intervention 1, 2
• Sphenopalatine ganglion block and radiofrequency ablation are additional options for refractory cases 2

When Structural Pathology is Present

• Immediate referral to otolaryngology for complete endoscopic examination, tissue biopsy, CT interpretation, and surgical planning if unilateral disease is confirmed 5
• Urgent biopsy with fungal staining and culture if invasive fungal disease is suspected in immunocompromised patients 5
• Surgical excision for inverted papillomas or other neoplasms identified on biopsy 5

Critical Pitfalls to Avoid

• Do not assume benign etiology without imaging in unilateral nasal symptoms, as malignancy and benign neoplasms are 7-8 times more likely with unilateral versus bilateral disease 4
• Do not delay evaluation in immunocompromised patients, as invasive fungal disease has 50-80% mortality without urgent intervention 5
• Do not miss unilateral polyps or masses on examination, as these mandate biopsy with a 4.5% diagnostic discrepancy rate 5
• Recognize that idiopathic external nasal neuralgia has poor response to intranasal anesthetics, suggesting central rather than peripheral etiology 2