Differential Diagnosis

Given the patient's symptoms of lynchified pus-filled pustules on the labia majora and negative screening results for common vaginal infections and STIs, the following differential diagnoses are considered:

• Single most likely diagnosis
  • Folliculitis: This condition, often caused by Staphylococcus aureus, presents with pus-filled pustules and can occur on the labia majora. The negative STI and vaginal infection screenings support this diagnosis, as folliculitis is not typically caused by the pathogens tested for.
• Other Likely diagnoses
  • Furuncles or Carbuncles: These are infections of the hair follicles that can become filled with pus, similar to the patient's symptoms. They are often caused by Staphylococcus aureus and can occur in the genital area.
  • Hidradenitis Suppurativa: Although less common, this chronic skin condition can cause pus-filled lesions in areas of the body with apocrine glands, including the genital area. The patient's symptoms could be consistent with a mild or early presentation of hidradenitis suppurativa.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Necrotizing Fasciitis: Although rare and less likely given the localized nature of the symptoms, necrotizing fasciitis is a life-threatening condition that requires immediate medical attention. It can present with skin lesions, pain, and swelling, and any delay in diagnosis can lead to severe consequences.
  • Malignancy: Certain types of skin cancers or metastatic disease could, in rare instances, present with skin lesions that might resemble the patient's symptoms. While unlikely, the possibility of malignancy should be considered, especially if the lesions do not respond to typical treatments or if there are other concerning signs or symptoms.
• Rare diagnoses
  • Kerion: A severe form of tinea capitis (ringworm of the scalp) that can rarely occur in the beard area or, even more rarely, in the genital area, causing pus-filled lesions.
  • Disseminated Gonococcal Infection (DGI): Although the gonorrhea screening was negative, DGI can present with skin lesions among other symptoms, and false negatives can occur, especially if the sample was not properly collected or if the infection is in an early stage.