Differential Diagnosis for 2-year-old Patient with Fever, Perianal Itching, and Loose Motions

Single Most Likely Diagnosis

• Pinworm Infestation (Enterobius vermicularis): This is the most common cause of perianal itching in children, often accompanied by fever and gastrointestinal symptoms like loose motions. The presence of perianal itching, especially at night, is highly suggestive of pinworms.

Other Likely Diagnoses

• Bacterial Gastroenteritis: Various bacteria can cause gastroenteritis, leading to symptoms like fever, loose motions, and potentially perianal irritation due to frequent diarrhea.
• Fungal Infections (e.g., Candidiasis): Candida can cause perianal itching and irritation, especially in the context of diarrhea or antibiotic use, which might alter the normal flora.
• Eczema/Dermatitis: Perianal skin can be affected by eczema or dermatitis, leading to itching and irritation, potentially exacerbated by loose motions.

Do Not Miss Diagnoses

• Inflammatory Bowel Disease (IBD): Although less common in this age group, conditions like Crohn's disease or ulcerative colitis can present with chronic diarrhea, fever, and perianal disease (e.g., fistulas, abscesses). Missing this diagnosis could lead to significant morbidity.
• Intussusception: A condition where a part of the intestine slides into an adjacent part, which can cause intestinal obstruction, fever, and potentially perianal symptoms if there's associated rectal bleeding or prolapse. It's a surgical emergency.
• Appendicitis: While less common in toddlers, appendicitis can present with fever, abdominal pain, and changes in bowel habits. Perianal itching is not a typical symptom, but if the appendix is located near the rectum, it could potentially cause perianal discomfort.

Rare Diagnoses

• Threadworms (Strongyloides stercoralis): A parasitic infection that can cause gastrointestinal symptoms and perianal itching, though it's less common than pinworms in this clinical context.
• Schistosomiasis: In endemic areas, schistosomiasis can cause gastrointestinal and perianal symptoms due to the parasitic infection, but it's rare in a 2-year-old without specific exposure history.
• Allergic Proctitis: An allergic reaction to certain foods can cause proctitis, leading to symptoms like perianal itching and rectal bleeding, especially in infants and young children.