What is the likely diagnosis for an adult or adolescent patient presenting with a unilateral periorbital dull ache that is throbbing, accompanied by a mild increase in tearing, without congestion, discharge, or fever?

Unilateral Periorbital Throbbing Pain with Tearing: Likely Diagnosis

The most likely diagnosis is cluster headache, which characteristically presents with severe unilateral periorbital pain accompanied by ipsilateral autonomic features including lacrimation, and this diagnosis should be strongly considered given the absence of infectious signs. 1, 2

Primary Diagnostic Considerations

Cluster Headache (Most Likely)

• Cluster headache presents with severe unilateral periorbital or supraorbital pain lasting 15-180 minutes and must have ipsilateral autonomic features including lacrimation, nasal congestion, rhinorrhea, ptosis, miosis, or eyelid edema. 1
• The throbbing, dull ache quality with increased tearing fits this diagnosis, particularly given the unilateral presentation without fever or discharge. 2
• Patients with cluster headache tend to be restless during attacks, distinguishing them from migraine patients who prefer to remain still. 2
• The absence of nasal congestion does not exclude cluster headache, as only one ipsilateral autonomic feature is required for diagnosis. 1, 2

Migraine Without Aura (Alternative Consideration)

• Migraine requires at least 2 of the following: unilateral location, pulsating quality, moderate-to-severe intensity, or aggravation by routine activity. 1
• The throbbing quality and unilateral location are consistent with migraine. 3
• However, migraine typically presents with photophobia and phonophobia rather than prominent lacrimation alone. 3, 1

Critical Red Flags to Exclude Immediately

Vision-Threatening Emergencies

• Perform a focused neurological examination checking visual acuity, extraocular movements, proptosis, pupil reactivity, and fundoscopic examination for papilledema. 1, 4
• Any abnormality on cranial nerve examination mandates neuroimaging. 1
• Check for proptosis, visual changes, or abnormal extraocular movements, which suggest orbital or intracranial complications requiring emergent MRI. 3, 1

Infectious Causes to Rule Out

• The absence of purulent discharge, nasal obstruction, and fever makes acute bacterial rhinosinusitis unlikely. 3, 1
• The absence of conjunctival injection, vesicular rash, or eyelid lesions makes viral conjunctivitis, HSV, or VZV infection unlikely. 4
• Preseptal or orbital cellulitis is excluded by the absence of fever, eyelid erythema/edema, and painful eye movements. 4

Diagnostic Algorithm

Step 1: Rule Out Red Flags

• Perform fundoscopic examination to check for papilledema indicating increased intracranial pressure. 1
• Complete cranial nerve examination to detect any neurological deficits. 1
• Assess for proptosis and extraocular movement abnormalities. 1, 4

Step 2: Characterize Pain Pattern

• Determine attack duration (cluster headache: 15-180 minutes; migraine: 4-72 hours). 3, 1, 2
• Assess for circadian or circannual periodicity (cluster headache often occurs at specific times, especially at night). 2
• Evaluate patient behavior during attacks (restlessness suggests cluster headache; preference for stillness suggests migraine). 2

Step 3: Identify Autonomic Features

• Document presence of lacrimation (present in this case). 1, 2
• Check for nasal congestion, rhinorrhea, ptosis, miosis, or eyelid edema on the affected side. 1, 2
• Note that only one ipsilateral autonomic feature is required for cluster headache diagnosis. 1

Management Approach

If Cluster Headache is Confirmed

• Acute treatment is based on subcutaneous sumatriptan and high-flow oxygen (100% oxygen at 12-15 L/min for 15 minutes). 2
• Prophylactic treatment includes verapamil as first-line, with lithium, methysergide, prednisone, or topiramate as alternatives. 2
• Avoid alcohol during cluster periods, as it is the only dietary trigger consistently identified. 2

If Migraine is Suspected

• Acute treatment with triptan combined with NSAID or acetaminophen, plus antiemetic. 1
• Limit acute medication use to ≤10 days per month to prevent medication overuse headache. 1

If Red Flags Present

• Obtain emergent MRI and consider immediate specialist consultation. 1
• Rapidly increasing frequency of headaches or atypical patterns warrant neuroimaging. 3

Critical Follow-Up Parameters

• Reassess immediately if high fever develops, severe facial pain worsens, neurological symptoms appear, or visual changes occur. 1
• If diagnosis remains uncertain after initial evaluation, consider neurology or ophthalmology referral for specialized assessment. 3, 1
• Document attack frequency, duration, and response to treatment to guide ongoing management. 2