Differential Diagnosis for Prolonged APTT, Reduced C3, and Livedoid Rash
- Single Most Likely Diagnosis
- Antiphospholipid Syndrome (APS): This condition is characterized by a combination of thrombosis, prolonged APTT due to the presence of lupus anticoagulant, and sometimes reduced complement levels like C3. The livedoid rash can be a manifestation of the thrombotic events associated with APS.
- Other Likely Diagnoses
- Systemic Lupus Erythematosus (SLE): SLE can cause a prolonged APTT due to lupus anticoagulant, reduced complement levels (including C3) due to consumption during inflammation, and skin manifestations that could include a livedoid rash.
- Thrombotic Thrombocytopenic Purpura (TTP): Although TTP primarily presents with thrombocytopenia, microangiopathic hemolytic anemia, renal failure, neurological symptoms, and fever, some cases might have a prolonged APTT and livedoid rash due to the thrombotic microangiopathy.
- Do Not Miss Diagnoses
- Disseminated Intravascular Coagulation (DIC): This is a condition characterized by both widespread clotting and bleeding in the vascular system, which can lead to a prolonged APTT, reduced complement levels due to consumption, and livedoid rash due to skin infarcts. Missing DIC could be fatal due to its high mortality rate if not promptly treated.
- Hemolytic Uremic Syndrome (HUS): Similar to TTP, HUS involves thrombotic microangiopathy but is more commonly associated with renal failure and less with neurological symptoms. It could present with a livedoid rash and coagulation abnormalities, including a prolonged APTT.
- Rare Diagnoses
- Atypical Hemolytic Uremic Syndrome (aHUS): This is a rare condition that presents similarly to HUS but without the typical diarrheal illness trigger. It can cause thrombotic microangiopathy, leading to a prolonged APTT, reduced complement levels (especially if associated with complement pathway mutations), and livedoid rash.
- C3 Glomerulopathy: This group of rare diseases is characterized by complement dysregulation leading to reduced C3 levels. While primarily affecting the kidneys, systemic manifestations could potentially include a livedoid rash and coagulation abnormalities, although this would be less common.