Differential Diagnosis for Elderly Man with Petechiae, Ecchymoses, and Haematuria

Single Most Likely Diagnosis

• Immune Thrombocytopenic Purpura (ITP): This condition is characterized by low platelet count due to immune-mediated destruction, which can be triggered by the flu vaccine. The presentation of petechiae, ecchymoses, and haematuria is consistent with ITP, especially given the recent vaccination.

Other Likely Diagnoses

• Vasculitis: Conditions like leukocytoclastic vasculitis can present with similar skin findings and can be triggered by infections or vaccinations. The presence of haematuria also suggests possible renal involvement.
• Disseminated Intravascular Coagulation (DIC): Although less common, DIC can present with bleeding manifestations, including petechiae and ecchymoses, and can be triggered by severe infections or other systemic conditions.
• Thrombotic Thrombocytopenic Purpura (TTP): This rare disorder of the blood-coagulation system can cause thrombocytopenia, microangiopathic hemolytic anemia, and renal failure, which might explain the haematuria.

Do Not Miss Diagnoses

• Henoch-Schönlein Purpura (HSP): A form of vasculitis that can present with purpura, arthritis, abdominal pain, and renal involvement. It's crucial to consider HSP due to its potential for severe renal complications.
• Meningococcemia: Although the flu vaccine is not a typical trigger, meningococcemia can cause petechiae and ecchymoses as part of a severe, life-threatening infection. Early recognition is critical for survival.
• Sepsis: Any condition leading to sepsis can cause coagulopathy, leading to bleeding manifestations. Given the recent flu vaccine, an infection should be considered, especially if there are signs of systemic illness.

Rare Diagnoses

• Thrombocytopenia with Absent Radius (TAR) Syndrome: An extremely rare genetic disorder that affects platelet production and can cause thrombocytopenia, but it's unlikely given the acute presentation following vaccination.
• Hemolytic Uremic Syndrome (HUS): Similar to TTP, HUS can cause renal failure and thrombocytopenia but is more commonly associated with diarrheal illnesses caused by E. coli O157:H7.
• Platelet Function Disorders: Such as Bernard-Soulier syndrome or Glanzmann thrombasthenia, which are rare genetic disorders affecting platelet function and could potentially be unmasked by a triggering event like vaccination, though they are less likely given the acute onset.