Differential Diagnosis
The patient presents with abdominal pain, vomiting, dark stools, decreased appetite, rash, and a history of recent travel and camping. The laboratory results show mild anemia, thrombocytosis, and elevated erythrocyte sedimentation rate. Based on these findings, the differential diagnosis can be categorized as follows:
Single most likely diagnosis
- Henoch-Schönlein Purpura (HSP): The presence of abdominal pain, vomiting, dark stools, and a rash characterized by purple non-blanching lesions (purpura) on the thighs, along with the laboratory findings, strongly suggests HSP. This condition is a form of vasculitis that affects small blood vessels and is often seen in young adults.
Other Likely diagnoses
- Inflammatory Bowel Disease (IBD): The symptoms of abdominal pain, vomiting, and dark stools could also be indicative of IBD, such as Crohn's disease or ulcerative colitis. However, the presence of purpura and the specific pattern of laboratory abnormalities make HSP more likely.
- Vasculitis (other forms): Other forms of vasculitis, such as microscopic polyangiitis or granulomatosis with polyangiitis, could present with similar symptoms, but the distribution of the rash and the absence of other systemic symptoms make them less likely.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Abdominal Aortic Aneurysm or Dissection: Although less likely given the patient's age and presentation, an abdominal aortic aneurysm or dissection could cause abdominal pain and vomiting. The absence of back pain and a murmur makes this less likely, but it is a critical diagnosis not to miss due to its high mortality rate.
- Infectious Causes (e.g., bacterial endocarditis): Despite the lack of fever, chills, or a murmur, infectious causes such as bacterial endocarditis could present with systemic symptoms including rash and abdominal pain. The patient's history of travel and camping increases the risk of certain infections.
Rare diagnoses
- Thrombotic Thrombocytopenic Purpura (TTP): TTP is a rare disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, renal failure, and neurological symptoms. While the patient has thrombocytosis rather than thrombocytopenia, and lacks other key features of TTP, it remains a rare consideration.
- Malignancy (e.g., lymphoma): Certain malignancies, such as lymphoma, can present with a wide range of systemic symptoms including rash, abdominal pain, and weight loss. However, the patient's age, lack of significant weight loss, and specific pattern of symptoms make this a less likely, though not impossible, diagnosis.