Differential Diagnosis for Acute Swelling of Eyelash Follicles

Single Most Likely Diagnosis

• Hordeolum (Stye): The patient's symptoms, including a painful, erythematous swelling that started as a possible stye approximately 1 week ago, with crusty discharge and no evidence of conjunctivitis, are highly suggestive of a hordeolum. This condition is an acute, localized infection or inflammation of the eyelash follicle or associated glands.

Other Likely Diagnoses

• Blepharitis: This is an inflammation of the eyelids that can cause redness, itching, and swelling, and can be associated with crusty discharge. It could be a contributing factor or a differential to consider, especially if the condition does not fully resolve with treatment for a stye.
• Meibomian Gland Dysfunction: While more common in adults, this condition can cause inflammation and blockage of the meibomian glands, leading to symptoms similar to a stye, including erythema and discharge.
• Demodex Infestation: Demodex mites can infest the eyelash follicles, leading to inflammation, erythema, and sometimes a crusty discharge. This is less common but should be considered, especially in recurrent cases.

Do Not Miss Diagnoses

• Orbital Cellulitis: Although less likely given the localized nature of the symptoms, orbital cellulitis is a serious infection of the tissues surrounding the eye that requires prompt treatment. It can present with eyelid swelling, erythema, and sometimes discharge, but typically is accompanied by more severe symptoms such as fever, proptosis, and limited eye movement.
• Preseptal Cellulitis: Similar to orbital cellulitis but less severe, preseptal cellulitis involves infection of the eyelid and periorbital tissues anterior to the orbital septum. It can present with swelling, redness, and sometimes discharge, and while it may seem similar to a stye, it requires broader antibiotic coverage.

Rare Diagnoses

• Molluscum Contagiosum: A viral infection that can cause small, pearly, or flesh-colored lesions on the eyelid, sometimes associated with conjunctivitis or keratitis. It's less likely given the description but could be considered in the differential, especially if the lesion does not respond to typical stye treatment.
• Leishmaniasis: In endemic areas, Leishmaniasis can cause eyelid lesions. However, this would be extremely rare and typically associated with systemic symptoms or a history of travel to endemic areas.