History of Present Illness (HPI)

The patient is a 5-year-old child whose mother is concerned about the presence of worms in the stool and reports a rash on the chest. The mother's concern about worms in the stool could indicate a parasitic infection, while the rash on the chest could be related to the infection or an allergic reaction. The child's age and symptoms suggest an infection that is common in pediatric populations.

Differential Diagnosis

Single Most Likely Diagnosis

• Pinworms (Enterobius vermicularis): This is a common parasitic infection in children, characterized by the presence of worms in the stool, perianal itching, and sometimes a rash. The age of the patient and the symptoms described make this a highly plausible diagnosis.

Other Likely Diagnoses

• Hookworms: Another type of parasitic infection that can cause gastrointestinal symptoms and a rash, although it's less common in developed countries.
• Roundworms (Toxocara or Ascaris): These can also cause gastrointestinal symptoms and, in some cases, a rash, especially if there's an allergic reaction to the parasites.
• Eczema or Atopic Dermatitis: The rash on the chest could be unrelated to the parasitic infection and might be a manifestation of eczema, especially if the child has a history of allergies or asthma.

Do Not Miss Diagnoses

• Strongyloidiasis: A parasitic infection that can cause a rash (larva currens) and gastrointestinal symptoms. It's less common but can be severe, especially in immunocompromised patients.
• Scabies: While primarily causing skin symptoms, scabies can lead to secondary infections and should be considered, especially if the rash is severe or accompanied by intense itching.

Rare Diagnoses

• Whipworm (Trichuris trichiura): Less common in developed countries, whipworm infection can cause gastrointestinal symptoms and, rarely, a rash.
• Tapeworms: Various species can infect humans, but they are less likely to cause the combination of symptoms described, especially the rash on the chest.

Each of these diagnoses should be considered based on the patient's full clinical presentation, including any additional symptoms, travel history, and exposure risks. Diagnostic tests, such as stool examinations for ova and parasites, and possibly skin scrapings or blood tests, may be necessary to confirm the diagnosis.