What is the likely cause of an elderly male patient's left under eye swelling, soreness, and left-sided mouth pain, given his complex medical history including hypertension, diabetes, chronic kidney disease, and others, and his current smokeless tobacco use?

Differential Diagnosis: Left Periorbital and Oral Pain in Elderly Patient

The most likely diagnosis in this elderly patient with left under-eye swelling, soreness, and left-sided mouth pain is preseptal cellulitis or maxillary sinusitis with periorbital extension, though malignancy (particularly sebaceous carcinoma or squamous cell carcinoma) must be urgently excluded given his age, smokeless tobacco use, and unilateral presentation. 1, 2

Immediate Red Flag Assessment

Before proceeding with differential diagnosis, you must immediately assess for orbital cellulitis by examining for:

• Proptosis
• Restricted or painful extraocular movements
• Vision changes or decreased visual acuity
• Severe pain with eye movement
• Fever with systemic toxicity 2, 3

If any of these signs are present, hospitalize immediately for IV antibiotics, obtain contrast-enhanced CT of orbits and sinuses, and consult ophthalmology, otolaryngology, and infectious disease urgently. 2

Most Likely Infectious Etiologies

Preseptal Cellulitis

This is a common cause of upper eyelid swelling in elderly patients and presents with:

• Periorbital edema and erythema
• Tenderness without orbital signs
• Normal extraocular movements and vision 2, 3

For mild preseptal cellulitis without orbital involvement, start high-dose oral amoxicillin-clavulanate with mandatory daily follow-up within 24-48 hours until definite improvement. 2, 3 Hospitalize for IV antibiotics if no improvement in 24-48 hours or if infection progresses. 2

Maxillary Sinusitis with Periorbital Extension

Given the left-sided mouth pain, maxillary sinusitis is highly relevant and characteristically presents with:

• Pain before eating (if salivary gland involved)
• Purulent nasal discharge
• Facial tenderness
• Medial canthal swelling
• Upper dental pain or recent dental procedures 4

The patient's diabetes and chronic kidney disease increase infection risk. Maxillary sinusitis can occur after dental infection or upper molar/premolar extractions, potentially causing oral-antral fistula. 4

Critical Malignancy Considerations

Given this patient's age, smokeless tobacco use, and unilateral presentation, malignancy must be actively excluded. 1, 5, 6

Sebaceous Carcinoma

This is particularly concerning in elderly patients and can masquerade as chronic blepharoconjunctivitis. Red flags include:

• Hard, non-mobile tarsal mass with yellowish discoloration
• Chronic unilateral presentation unresponsive to treatment
• Focal lash loss
• Recurrent "chalazion" in the same location
• Pagetoid spread causing severe conjunctival inflammation 4, 1

Sebaceous carcinoma should be considered in elderly patients who have unresponsive, chronic, unilateral blepharitis or conjunctivitis. 4

Squamous Cell Carcinoma and Basal Cell Carcinoma

These are the most frequently encountered malignant eyelid tumors and may present with:

• Nodular mass
• Ulceration
• Extensive scarring
• Localized crusting and scaling
• Eyelid margin destruction or loss of lashes
• Papillomatous or sessile nodules 4, 1

Squamous cell carcinoma is associated with smokeless tobacco use, which this patient actively uses. 5, 6 Smokeless tobacco is associated with chronic diseases including hypertension, diabetes, and cancer—all present in this patient. 6

Oral Pain Differential

The left-sided mouth pain requires specific evaluation for:

Dental and Oral Causes

• Dental abscess or periapical infection
• Oral mucosal lesions (lichen planus, herpes simplex, oral ulceration)
• Diseases requiring good light examination of teeth, attached gingiva, and oral mucosa 4

Salivary Gland Disorders

• Submandibular stone or duct blockage
• Pain characteristically occurs just before eating
• Bimanual palpation may reveal stone
• Slow or absent salivary flow from duct 4

Temporomandibular Disorders (TMD)

• Most common non-dental cause of facial pain
• Affects 5-12% of population
• Peak age 20-40 years, but can occur in elderly
• Associated with depression, catastrophizing, back pain, fibromyalgia 4

Mandatory Examination Components

Perform focused examination including:

• Visual acuity testing
• Extraocular movement assessment
• Pupillary examination
• Eversion of upper eyelid to examine tarsal conjunctiva
• Fluorescein staining to rule out corneal involvement
• Palpation for focal tenderness or nodules
• Examination of teeth, gingiva, and oral mucosa with good light
• Bimanual palpation of salivary glands 4, 3

Clinical Algorithm

Step 1: Rule out orbital cellulitis (if present → immediate hospitalization) 2, 3

Step 2: Examine for malignancy red flags:

• Gradual enlargement over weeks to months
• Central ulceration or induration
• Irregular borders
• Eyelid margin destruction or loss of lashes
• Chronic unilateral presentation unresponsive to standard therapy
• Marked asymmetry or unifocal recurrence 1

If any malignancy red flags present → immediate biopsy with urgent ophthalmology referral. 1 Fresh tissue may be required for special stains such as oil red-O for lipid detection in sebaceous carcinoma. 1

Step 3: If infectious etiology suspected without orbital involvement:

• Start high-dose amoxicillin-clavulanate
• Daily follow-up within 24-48 hours mandatory
• Consider imaging if sinusitis suspected
• Dental referral if oral/dental source identified 4, 2, 3

Step 4: If no improvement in 24-48 hours or progressive infection → hospitalize for IV antibiotics 2, 3

Critical Pitfalls to Avoid

Do not start topical corticosteroids before ruling out infection, as this may worsen infectious processes or mask accurate diagnosis. 3

Do not dismiss chronic unilateral presentation as benign blepharitis—this is a red flag for sebaceous carcinoma in elderly patients. 4, 1

Do not overlook the patient's smokeless tobacco use as a significant risk factor for oral and periocular malignancies. 5, 6

Urgent Referral Indications

Urgent same-day ophthalmology referral for:

• Any signs of orbital cellulitis
• Vision changes
• Severe pain
• Suspected malignancy
• Chronic unilateral presentation unresponsive to initial treatment 1, 2, 3

Dental referral if:

• Dental source identified
• Oral mucosal lesions present
• Salivary gland pathology suspected 4