Differential Diagnosis

• Single most likely diagnosis
  • Perianal candidiasis: Given the patient's history of recurrent vulvovaginal fungal infections and the description of the itching sensation similar to a previous fungal infection, perianal candidiasis is a strong consideration. The worsening of symptoms with moisture and the presence of a burning sensation after washing with warm water also support this diagnosis.
• Other Likely diagnoses
  • Haemorrhoidal irritation: The patient's history of haemorrhoids could contribute to perianal itching, especially if the haemorrhoids are thrombosed or prolapsed, causing irritation and discomfort.
  • Contact dermatitis: Irritation from soaps, wipes, or other products used in the perianal area could cause itching and burning sensations, especially with prolonged wearing of pants and increased moisture.
  • Pruritus ani: A condition characterized by intense itching around the anus, which can be caused by various factors including dietary habits, hygiene practices, and skin conditions.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Anal cancer: Although rare, anal cancer can present with perianal itching and should be considered, especially in the absence of other obvious causes.
  • Inflammatory bowel disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause perianal itching, among other symptoms, and require prompt diagnosis and treatment to prevent complications.
  • STDs (e.g., herpes simplex, syphilis): Despite the patient's reported monogamous relationship and lack of STI history, the possibility of an undiagnosed or newly acquired infection should not be entirely ruled out without further investigation.
• Rare diagnoses
  • Lichen sclerosus: A rare skin condition that can cause itching and skin changes in the genital and perianal areas.
  • Lichen planus: An autoimmune condition that can affect the skin and mucous membranes, leading to itching and lesions in the perianal area.
  • Pinworms (Enterobius vermicularis): Although more common in children, pinworm infestation can cause perianal itching in adults, especially if there is a history of exposure to infected individuals.