Differential Diagnosis
- Single most likely diagnosis
- Pilonidal sinus or cyst: The patient's symptoms of blood and discharge that have settled at the anal cleft, along with mild swelling to the bottom left under the skin, are consistent with a pilonidal sinus or cyst. The location and nature of the symptoms strongly suggest this diagnosis.
- Other Likely diagnoses
- Perianal abscess: The presence of discharge and swelling near the anal cleft could also indicate a perianal abscess, which is a collection of pus in the tissue around the anus.
- Anal fistula: An anal fistula, an abnormal connection between the inside of the anus and the skin around it, could also cause discharge and swelling, although it might not fully account for the settling of discharge at the anal cleft.
- Infected anal gland: Infection of the anal glands can cause symptoms similar to those described, including discharge and swelling.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Rectal cancer: Although less likely given the patient's age and lack of other symptoms like weight loss or persistent bleeding, rectal cancer can cause similar symptoms and is critical to rule out due to its severity.
- Necrotizing fasciitis: This is a rare but life-threatening infection of the skin and soft tissues. The presence of swelling and discharge, even without systemic symptoms like fever, warrants consideration of this diagnosis due to its potential severity.
- Rare diagnoses
- Hidradenitis suppurativa: This chronic skin condition can cause abscesses and nodules in the apocrine-gland-bearing areas of the body, including the perianal region, but it typically involves more widespread lesions and a longer history of symptoms.
- Crohn's disease or ulcerative colitis with perianal involvement: These inflammatory bowel diseases can cause a variety of perianal symptoms, including fistulas, abscesses, and swelling, but are usually accompanied by gastrointestinal symptoms like diarrhea or abdominal pain.