Differential Diagnosis for a Single Closed Pustule on the Face

• Single Most Likely Diagnosis
  • Acne vulgaris: This is the most common skin condition and can present with a single pustule, especially during puberty or in individuals with a history of acne. The pustule is typically closed and not leaking.
• Other Likely Diagnoses
  • Folliculitis: An infection of the hair follicle, which can appear as a single pustule, often caused by Staphylococcus aureus. It's common in areas with high hair density like the face.
  • Furuncle (Boil): A deeper infection of the hair follicle that can present as a single, painful pustule. It's usually caused by Staphylococcus aureus.
  • Keratosis pilaris: While typically presenting with multiple small bumps, a single lesion could be considered, especially if the pustule is small and on an area like the cheek.
• Do Not Miss Diagnoses
  • Cellulitis: Although it usually presents with more widespread erythema and swelling, a localized, early infection could mimic a single pustule. It's crucial to monitor for signs of spreading infection.
  • Erysipelas: A type of superficial cellulitis that can start as a small, raised, red lesion and can be mistaken for a pustule. It requires prompt antibiotic treatment.
  • Methicillin-resistant Staphylococcus aureus (MRSA) infection: MRSA can cause skin infections that may appear as pustules, and it's essential to consider this diagnosis, especially if the lesion does not respond to standard treatments.
• Rare Diagnoses
  • Lupus miliaris disseminatus faciei (LMDF): A rare condition characterized by multiple small, reddish-brown papules or pustules on the face, which could potentially be mistaken for a single pustule if only one lesion is present.
  • Sarcoidosis: Although it more commonly presents with multiple lesions, a single pustule could be a rare manifestation, especially if it's part of a systemic disease.
  • Leishmaniasis: In endemic areas, cutaneous leishmaniasis can present with a single skin lesion that might resemble a pustule, although it typically progresses to an ulcer.