What is the most likely diagnosis for a 69-year-old man with myelodysplastic syndrome (MDS) who develops generalized pruritus and urticaria after receiving a blood transfusion, with a mild fever and otherwise normal vital signs?

Differential Diagnosis for the 69-year-old man with myelodysplastic syndrome

• Single most likely diagnosis: + Allergic reaction to blood transfusion: This is the most likely diagnosis given the symptoms of generalized itching, hives, and a mild fever that occurred shortly after the blood transfusion. These symptoms are consistent with an allergic reaction, which can range from mild to severe and are a known complication of blood transfusions.
• Other Likely diagnoses: + Transfusion-related acute lung injury (TRALI): Although less common, TRALI is a possibility, especially if the patient develops respiratory symptoms. However, the current symptoms do not strongly suggest TRALI, as it typically presents with more severe respiratory distress. + Anaphylactoid reaction: Similar to an allergic reaction but does not involve an immune-mediated response. It can present with similar symptoms but is less likely given the context of a blood transfusion.
• Do Not Miss diagnoses: + Anaphylaxis: A severe, life-threatening allergic reaction that requires immediate intervention. Although the patient's symptoms are currently mild, anaphylaxis can progress rapidly, and it is crucial to monitor the patient closely for any signs of worsening. + Bacterial contamination of the blood product: This is a rare but potentially deadly complication of blood transfusions. Symptoms can include fever, chills, and potentially severe sepsis. Given the patient's fever, this diagnosis must be considered and ruled out. + Hemolytic transfusion reaction: Although the patient's symptoms do not currently suggest a hemolytic reaction (which would typically include more severe symptoms such as hypotension, severe pain, and potentially jaundice), it is a critical diagnosis not to miss due to its high mortality rate.
• Rare diagnoses: + Transfusion-associated circulatory overload (TACO): This condition is characterized by respiratory distress, hypoxia, and often signs of heart failure, which are not currently present in this patient. + Graft-versus-host disease (GVHD): Although extremely rare in the context of blood transfusions (more commonly associated with bone marrow or solid organ transplants), GVHD can occur, especially in immunocompromised patients. However, the symptoms described do not align closely with GVHD, which typically includes rash, liver dysfunction, and gastrointestinal symptoms.