Differential Diagnosis for a 16-year-old boy with Crohn disease, diarrhea, and rash
- Single most likely diagnosis:
- Nutritional deficiency: Given the patient's Crohn disease, which can lead to malabsorption, and symptoms such as watery diarrhea, smooth red tongue (suggestive of vitamin B12 deficiency), and a rash, a nutritional deficiency (e.g., niacin, vitamin B12, or zinc deficiency) is a plausible explanation. The rash described, with its characteristics of being dry, erythematous, hyperpigmented, and having sharp lines of demarcation, could be consistent with pellagra (niacin deficiency), which also causes dermatitis, diarrhea, dementia, and potentially death if not treated.
- Other Likely diagnoses:
- Perianal disease or fistulae: Complications of Crohn disease that could cause diarrhea and potentially lead to skin manifestations due to bacterial or fungal infections.
- Inflammatory bowel disease (IBD) exacerbation: The patient's symptoms of diarrhea could indicate an exacerbation of his Crohn disease, and the rash might be an extraintestinal manifestation of IBD.
- Medication side effects: If the patient is on any medications for his Crohn disease, some of these could potentially cause diarrhea and skin rashes as side effects.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Neurological complications of vitamin B12 deficiency: While less likely, a deficiency in vitamin B12 can lead to neurological symptoms, including difficulty concentrating and changes in mood or interest in activities, which could be mistaken for other conditions but are critical to identify due to their potential for irreversible damage if left untreated.
- Sepsis or severe infection: Although the patient's vital signs are normal, the presence of a rash and diarrhea in a patient with a chronic condition like Crohn disease necessitates consideration of severe infections, which could be life-threatening.
- Rare diagnoses:
- Erythema nodosum or pyoderma gangrenosum: These are rare skin conditions associated with IBD but could explain the rash.
- Dermatitis herpetiformis: An autoimmune blistering disorder associated with celiac disease, which could present with a rash and gastrointestinal symptoms, although it's less likely given the patient's known diagnosis of Crohn disease.
- Zinc deficiency (acrodermatitis enteropathica): A rare genetic disorder leading to zinc deficiency, characterized by skin lesions, diarrhea, and other symptoms, which could be considered in the differential diagnosis of a patient with Crohn disease and malabsorption.