Differential Diagnosis
The patient presents with below the knee swelling, bruising after a knee injury, and fatigue. Given the laboratory results, including a CBC, CMP, BNP, and D-dimer, we can categorize the differential diagnoses as follows:
Single Most Likely Diagnosis
- Traumatic injury with hematoma: The patient's history of hitting her knee and subsequent bruising and swelling below the knee makes a traumatic injury with hematoma the most likely diagnosis. The unremarkable CBC and CMP, along with a low BNP and D-dimer, do not strongly suggest other acute conditions.
Other Likely Diagnoses
- Deep Vein Thrombosis (DVT): Although the D-dimer is low, which makes DVT less likely, it cannot be entirely ruled out, especially if the patient has other risk factors. The swelling and bruising could be consistent with a DVT, but further testing like ultrasound would be needed for diagnosis.
- Cellulitis: The swelling and bruising could also be signs of cellulitis, especially if there's an open wound from the injury. However, the absence of fever or elevated white blood cell count makes this less likely.
- Fatigue could be related to various factors, including anemia (though the CBC is unremarkable), viral infections, or other non-specific causes.
Do Not Miss Diagnoses
- Pulmonary Embolism (PE): Although the BNP and D-dimer are not elevated, a PE can sometimes present with atypical symptoms, and missing it could be fatal. The recent onset of fatigue could be a symptom, but without other signs like shortness of breath or chest pain, it's less likely.
- Compartment Syndrome: This is a serious condition that could result from a traumatic injury, especially if there's significant swelling. It requires immediate attention to prevent long-term damage.
Rare Diagnoses
- Rhabdomyolysis: This condition, characterized by muscle breakdown, could potentially occur after significant trauma. However, it would typically present with elevated creatine kinase levels on the CMP, which is not mentioned.
- Neoplastic conditions: Rarely, unexplained swelling and fatigue could be signs of a neoplasm, but this would be an unlikely initial presentation without other systemic symptoms or abnormal laboratory findings.