BACKGROUND: Idiopathic thrombotic thrombocytopenic purpura (TTP) is a rare 
hematological emergency characterized by the pentad of microangiopathic 
hemolytic anemia, thrombocytopenia, neurological symptoms, renal injury, and 
fever that is invariably fatal if left untreated. Prompt intervention with 
plasma exchange minimizes mortality and is the cornerstone of therapy. Rare 
reports have described "pseudo-TTP" driven by extreme hematologic abnormalities 
resulting from deficiency of vitamin B12. Distinguishing between these entities 
can pose a diagnostic and therapeutic challenge.
CASE PRESENTATION: A 77 year old female presented with altered mental status, 
renal insufficiency, thrombocytopenia and evidence of microangiopathic hemolytic 
anemia, suggesting TTP. Workup demonstrated macrocytosis and reticulocytopenia, 
and B12 level was unmeasurably low. Other elements of her clinical presentation, 
including volume loss and bleeding suggested a multifactorial pathogenesis could 
be contributing to her laboratory abnormalities, reducing the likelihood that 
she had TTP. The risks and benefits of treating aggressively with therapeutic 
plasma exchange (TPE) for TTP were considered given the diagnostic 
possibilities. The patient received TPE initially, with rapid de-escalation 
after her clinical response suggested "pseudo-TTP" from B12 deficiency was the 
driving the process. B12 supplementation corrected her hematologic abnormalities 
and she remains well two years after presenting.
CONCLUSIONS: TTP is a rare condition with fatal consequences if left untreated. 
Guidelines recommend TPE even if there is uncertainty about the diagnosis of 
TTP. B12 deficiency is common, though not typically associated with severe 
hematologic abnormalities. We compare the presenting characteristics of all 
thirteen cases of pseudo-TTP reported in the literature with those from patients 
in case series of TTP to suggest a set of parameters that can help clinicians 
distinguish between pseudo-TTP and TTP and guide decision making regarding 
intervention. Evaluation of all TTP cases should include a B12, methylmalonic 
acid level and reticulocyte count. Reticulocytopenia suggests B12 deficiency. 
Finally an LDH level above 2500 IU/L is relatively uncommon in TTP and should 
suggest consideration of B12 deficiency.