Differential Diagnosis for a 23-year-old Patient with Dysuria and Vulvar Burning

• Single most likely diagnosis:
  • Herpes Simplex Virus (HSV) infection: The patient's symptoms of dysuria, vulvar burning, and a visible lesion resembling a "cut" or "ingrown hair" that is painful to touch, especially after a new sexual partner, are highly suggestive of a genital herpes infection. The negative urine test for UTI and the absence of other symptoms like vaginal discharge or odor further support this diagnosis.
• Other Likely diagnoses:
  • Bartholin gland cyst or abscess: The description of a painful lesion could also be consistent with a Bartholin gland cyst or abscess, especially if the patient has recently become sexually active with a new partner, potentially introducing new bacteria.
  • Syphilitic chancre: Although less common, a syphilitic chancre can present as a single, painful lesion, and the patient's recent new sexual partner increases the risk of sexually transmitted infections (STIs).
  • Vulvar folliculitis or ingrown hair: Given the patient's description of the lesion as possibly an "ingrown hair" and the presence of vulvar burning, folliculitis or an ingrown hair could be considered, though the pain upon touching and the context of recent sexual activity with a new partner make this less likely.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed):
  • Necrotizing fasciitis: Although extremely rare, necrotizing fasciitis is a life-threatening condition that can present with severe pain, swelling, and skin lesions. The patient's complaint of pain upon touching the area and the presence of a lesion warrant consideration of this diagnosis to ensure prompt recognition and treatment.
  • Malignancy: Though uncommon in young women, vulvar cancer or other malignancies could present with a painful lesion. Given the patient's age and the absence of other risk factors, this is less likely but should not be entirely dismissed without further evaluation.
• Rare diagnoses:
  • Behçet's disease: This rare condition can cause genital ulcers that are painful, along with other systemic symptoms. However, the patient's presentation lacks other typical symptoms of Behçet's, such as oral ulcers or eye inflammation.
  • Aphthous ulcers or other autoimmune conditions: These could potentially cause painful genital lesions, but they are less common and would typically be associated with other systemic or mucocutaneous symptoms.