Adult Vitamin B12 Deficiency-Associated Pseudo-Thrombotic Microangiopathy: A Systematic Review of Case Reports

Cobalamin-deficient thrombotic microangiopathy or vitamin B12 deficiency presenting as pseudo-thrombotic microangiopathy is a rare disorder that can be misdiagnosed as thrombotic thrombocytopenic purpura. Patients with this condition are at risk of receiving unnecessary plasmapheresis with a potential delay in appropriate therapy with vitamin B12 supplementation. There are no established diagnostic criteria for this condition in clinical practice. We performed a systematic review of case reports published between January 2018 and January 2023 to analyze the clinical characteristics, risk factors, and patterns of laboratory markers to improve the diagnostic criteria for this condition.


Introduction And Background
Vitamin B12 deficiency can present as pseudo-thrombotic microangiopathy (pseudo-TMA) that mimics thrombotic thrombocytopenic purpura (TTP) [1].TTP is a life-threatening medical condition that results from a deficiency of ADAMTS13, a metalloproteinase enzyme that cleaves von Willebrand factor (vWF).ADAMTS13 deficiency can be acquired secondary to autoantibodies or can be congenital due to the inability to synthesize the enzyme.Regardless of the mechanism, loss of ADAMTS13 activity results in ultra-large vWF multimers that trigger platelet activation and aggregation, leading to microthrombi and tissue ischemia.When left untreated, this condition carries a mortality rate of over 90%.The cornerstone of management is plasma exchange, which simultaneously removes circulating autoantibodies and replenishes ADAMTS13 levels.Timely initiation of this life-saving therapy is critical and typically based on the clinical picture of hemolysis with schistocytosis and severe thrombocytopenia [2].
Cobalamin-deficient thrombotic microangiopathy presents with macrocytic anemia and ineffective erythropoiesis, leading to intramedullary hemolysis resulting in elevated lactate dehydrogenase (LDH), low haptoglobin, and schistocytes in the peripheral blood smear.Thrombocytopenia can also occur due to inadequate bone marrow production.This clinical combination of anemia with an elevated LDH, schistocytosis, and thrmobocytopenia closely mimics the presentation of TTP.Cobalamin-deficient thrombotic microangiopathy is a relatively rare disorder with a prevalence estimates as low as 0.6% to 2.5% of all vitamin B12 deficiency cases [3].Due to its ambiguous presentation and comparative rarity, it is often misdiagnosed as TTP and treated inappropriately with plasmapheresis [4].This is unfortunate, as plasmapheresis, while life-saving in appropriate circumstances, does carry a risk of complications.Moreover, although vitamin B12 supplementation is the mainstay of therapy, it is often delayed because of failure to recognize vitamin B12 deficiency as the underlying etiology [5].Thus, early recognition and diagnosis of this condition can simultaneously prevent or limit the number of days on unnecessary plasma exchange and allow early initiation of appropriate and effective treatment.
Diagnosing vitamin B12 deficiency in patients presenting as pseudo-TMA requires thorough history taking, physical examination, and laboratory assessment.The PLASMIC score is a validated tool that can be used to screen for TTP as it correlates well with the ADAMTS13 level [6,7].Patients with vitamin B12 deficiencyassociated pseudo-TMA present with markers of hemolysis such as elevated LDH, as well as anemia and thrombocytopenia, and have a low vitamin B12 level, which is diagnostic [5,8].Due to overlapping features with TTP, these patients can have an elevated PLASMIC score.Thus, the PLASMIC score cannot be reliably used to exclude this condition.A retrospective cohort study conducted in 2020 attempted to establish specific diagnostic criteria.It recommended reticulocytopenia, markedly elevated LDH, and an absence of significant thrombocytopenia as potential criteria.Of note, tear drop cells were also frequently noted on peripheral smears aside from schistocytes, and could thus be considered as an additional criterion [9].

Literature Search
We followed the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) to conduct this review [10].V Ganipisetti and S Maringanti independently searched PubMed, Embase, and Web of Science databases.The search strategies we used for each database are presented in Table 1.

Science
Database search using keywords K Naha performed an additional manual search for relevant case reports and included 11 cases.K Naha and E Lingas sorted discrepancies.E Lingas compiled the final list for data extraction and analysis.

Inclusion and Exclusion Criteria
All case reports of adults with vitamin B12 deficiency presenting as thrombotic microangiopathy between January 2018 and January 2023 were included.
Exclusion criteria included pediatric cases, case reports without full text available, and articles not classified as case reports, such as review articles and letters to the editor.

Data Extraction and Quality Assessment
Full texts of all included case reports were reviewed.We used the Joanna Briggs Institute critical appraisal tool to assess included case reports [11].This tool consists of eight clearly defined and concise questions with four possible choices (yes, no, unclear, and not applicable).The number of "yes" answers for each study across the nine checklist selection criteria was counted and used for the overall inclusion of the study to reduce the risk of bias.A total of 46 case reports were ultimately included.Baseline demographic data, symptomatology, laboratory investigations, information on the etiology of vitamin B12 deficiency, treatment strategies, and final outcomes were extracted and compiled.

Search Selection Results
A preliminary search of bibliographic databases yielded 114 case reports (43 from PubMed, 29 from Embase, 42 from Web of Science) with potential relevance to the topic.A total of 33 articles were excluded due to duplication.Further, 44 articles were excluded based on the exclusion criteria and irrelevance after screening the titles and abstracts.Of the remaining 37 articles, one article was excluded as it was a letter to the editor, and three other articles were excluded as the clinical presentation was with hemolysis only without other features of TTP.From the remaining 33 articles, 35 cases were extracted as these included two case series each describing two cases by Ceuleers et al. [12] and Jahangiri et al. [13].An additional nine articles that The list of case reports included in our review and a summary of each case report are presented in

Demographics
The mean age of the included patients was 53.7 years (range = 17-90 years).More than half of the patients were male (63%), and 37% were female patients.

Comorbidities
A wide range of comorbidities were reported.Autoimmune comorbidities were reported in a few cases.Koontz et al. [32] reported a case with concomitant Graves' disease, Koubaissi et al. [33] reported Hashimoto's disease, Li et al. [36] reported vitiligo, and Chang et al. [19] reported a case of celiac disease.A few patients had a history of gastrectomy and alcoholism as comorbidities.Harada et al. [26] reported a history of gastric cancer, and Lee et al. [35] reported a history of lymphoma.

Symptomatology
Symptoms of this condition were mostly non-specific, such as fatigue, lightheadedness or dizziness, exertional dyspnea, and weakness.Some patients presented with neurological abnormalities, such as memory or cognitive issues, altered mental status, and paresthesias.Symptom onset could be days, weeks, or even a few months before presentation and diagnosis.

Laboratory Parameters
All included patients had low vitamin B12 levels, ranging from undetectable to 159 µ/L, with a mean level of 86.6 µ/L.Many patients presented with macrocytic anemia, with mean mean corpuscular volume (MCV) and hemoglobin values of 109.3 fL and 5 g/dL, respectively.Another notable laboratory abnormality was thrombocytopenia.Although the lowest platelet level observed was 8,000 cells/mm 3 , the mean platelet count at presentation was 77,400 cells/mm 3 .Elevated LDH was a common finding, with values ranging from 197 U/L to 9,894 U/L and a mean value of 3,165 U/L.Patients were also frequently found to have low haptoglobin.This combination of elevated LDH and depressed haptoglobin level is classically seen with hemolysis [53,54].In vitamin B12 deficiency, however, these findings reflect intramedullary hemolysis due to ineffective erythropoiesis.The mean PLASMIC score was 5, with a maximum PLASMIC score of 6.Seven patients had a score of 6. Abnormal coagulation parameters, such as an elevated international normalized ratio, were reported in a few patients.Other reported abnormalities included elevated homocysteine levels and positive direct Coomb's test in a few cases.The significance of these findings is unclear.A few included cases did not report PLASMIC scores, and we manually calculated values for them by reading the text and using available lab information.Reticulocyte index values were also not reported in a few case reports, and we did our final analysis on this using reported reticulocyte indexes only.The mean, median, maximum, and minimum values of relevant laboratory investigations were calculated and are presented in Table 3.

Etiology
In our review, pernicious anemia was the most commonly identified etiology (56.5 %) for cobalamindeficient thrombotic microangiopathy (26 out of 46 cases).Of the 46 case reports, six mentioned nutritional deficiency as an etiology.Of note, the case reported by Ganipisetti et al. also had concomitant thiamine deficiency [3], while the case reported by Ceuleers et al. had concomitant folate deficiency [12].Hussain et al. reported metformin use as the etiology [28], and Ricci et al. reported human immunodeficiency virusassociated loss of haptocorrin as the etiology [45].Chang et al. reported celiac disease as a possible etiology [19].One case each of autoimmune gastritis, Helicobacter pylori, and atrophic gastritis etiologies was reported [35,43,51].Other rare etiologies included gastric resection [26] and bowel resection [41].Five cases did not mention any specific etiology.

Treatment
All 46 cases received vitamin B12 treatments with improvement in clinical condition.Fifteen patients (32.6%) also received plasma exchange (PLEX).The patients reported by Ricci et al. and Gupta et al. also had concomitant TTP and received rituximab [25,45].Eight patients received steroids, one patient received eculizumab [40], and one patient received caplacizumab [12].

Discussion
Our review of cobalamin-deficient thrombotic microangiopathy cases revealed some key features that can help distinguish this disorder from TTP.The presence of risk factors for vitamin B12 deficiency, such as a strict vegetarian or vegan diet or poor nutrition, alcoholism, history of autoimmune diseases, gastrectomy, or gastric bypass, in a patient presenting with a TTP-like clinical picture should raise suspicion for cobalamin-deficient thrombotic microangiopathy.However, the absence of such factors cannot be used to rule out cobalamin deficiency, as the majority of patients in our review had undiagnosed pernicious anemia.Importantly, our review reinforced the clinical similarities between these two conditions, showing that symptomatology cannot be relied upon to distinguish between them.
Although the patients included in this review had laboratory findings of elevated LDH, low haptoglobin, and elevated indirect bilirubin similar to TTP, the degree of elevation of LDH was strikingly high compared to TTP.Our study showed a mean LDH of 3,165 U/L, whereas reviews of TTP have consistently shown elevated median LDH in the range of 1,107 to 1,750 U/L [55,56].Previously published systematic reviews of cobalamin-deficient thrombotic microangiopathy also showed similar findings of a high median LDH [5].
Another distinctive feature in these patients was the presence of relatively modest thrombocytopenia with a median of 64,000/µL, and a mean of 77,500/µL, compared to the severe thrombocytopenia seen with TTP [55,57].This finding likely reflects the underlying mechanism of inadequate production in contrast to the widespread thrombi formation leading to platelet consumption in TTP.Most patients in this review also presented with leukopenia with a median of 3.5 k//µL, often seen in severe vitamin B12 deficiency [58], but it is not a characteristic feature of TTP.
Of note, peripheral blood smears in most patients presented in this review demonstrated schistocytes, a hallmark of TTP.Taken along with biochemical features of hemolysis, this means that most of these cases fulfilled the criteria for microangiopathic hemolytic anemia (MAHA).The presence of hypersegmented neutrophils in peripheral smear should raise the suspicion of vitamin B12 deficiency.
The anemia observed in TTP results from intravascular hemolysis from MAHA and is associated with compensatory reticulocytosis due to bone marrow response to anemia.In contrast, even though cyanocobalamin deficiency can be associated with some features of hemolysis due to ineffective erythropoiesis, it is not associated with reticulocytosis and, indeed, usually presents with a hypoproliferative picture due to compromised marrow function.This phenomenon was reflected in the low reticulocyte index with a mean value of 0.9% seen in our review, which is consistent with a previous review [5].
Measurement of ADAMTS13 activity is the confirmatory test for the diagnosis of TTP [59], but it is often a send-out test and usually carries a slow turn-around time, which makes it impractical as a clinical decisionmaking tool when deciding whether to initiate PLEX.Bendapudi et al. [6] formulated a clinical scoring system called the PLASMIC score, which, when calculated, provides a low (4 and below), intermediate (5), or high (6 and above) probability of TTP.This allows rapid initiation of life-saving treatment for TTP while the ADAMTS13 level is awaited.
The median PLASMIC score for the patients in our review was 5, which falls under the intermediate category and necessitates initiation of treatment with plasmapheresis.In our review, we discovered that 15 patients received plasmapheresis, of whom five patients received concomitant systemic steroids.ADAMTS13 level was normal in all but two patients where TTP co-existed with vitamin B12 deficiency [25,45].Based on these findings, it appears that the PLASMIC score cannot be used to distinguish between these two disorders reliably.Instead, we propose a modified PLASMIC score incorporating the reticulocyte index into the calculation to overcome this shortcoming.In a previous systematic review by Tran et al., the maximum reticulocyte production index (RPI) in the cases reviewed was 1.57% [5], and, in our review, the maximum reported value was 2.7% (Gupta et al.), where the patient also had concomitant TTP [25].Usually, >3% RPI is considered a normal response to anemia [5].This modified score would award -1 points for a reticulocyte index of less than 3% and 0 points for over 3%.This would lower the score to 4 in most of our patients, reclassifying them as low-risk and saving them from unnecessary PLEX and immunosuppressive therapy.Moreover, even with this modification, the two patients with concurrent TTP and vitamin B12 deficiency would have still scored 5 and thus received appropriate treatment.However, due to limited information available so far, further larger-scale studies are needed to validate this modified PLASMIC score, specifically by applying it to the registry of TTP patients and comparing the sensitivity and specificity of this score against the original PLASMIC score.
All patients included in our review responded to vitamin B12 supplementation with clinical improvement.Some patients received plasmapheresis which was later stopped after ruling out TTP.A few patients received steroids as well with no change in their clinical status [20,43,47,48].

Strengths and limitations
This systematic review has several advantages.To our knowledge, it is the only systematic review encompassing cases of cobalamin-deficient microangiopathy since 2018.The relevance of this study is underscored by its potential to contribute to the ongoing conversation about rising healthcare costs in the United States.Furthermore, the findings of this study highlight the pressing need to establish updated diagnostic guidelines to minimize unnecessary treatments such as PLEX and immunosuppression in this patient population.
The primary limitation of this study is its retrospective nature.Being sourced exclusively from published case reports, it is subject to bias.Consequently, the findings of this study may not precisely represent diagnostic thresholds.Many real-world cases may go undiagnosed and unreported and thus absent from the published literature, introducing an element of bias.We also had to manually calculate the PLASMIC score for a few case reports based on the information available in the case reports, as the exact score was not reported in the full text of the articles.

Conclusions
Our systematic review adds to the medical literature on cobalamin-deficient thrombotic microangiopathy.Although uncommon, this condition can lead to diagnostic and clinical confusion because of several similarities that it shares with TTP.Our review supports the contention that patients with features of hemolytic anemia should be evaluated for vitamin B12 deficiency and that low vitamin B12 levels in such cases should be promptly managed by appropriate supplementation because of the high likelihood of reversing the pathologic process.Patients with cobalamin-deficient thrombotic microangiopathy tend to have higher LDH and platelet levels than those seen with true TTP and a lower reticulocyte index indicating a hypoproliferative bone marrow.We also found several case reports with normal MCV, indicating the importance of testing for vitamin B12 deficiency in these patients regardless of the MCV.We suggest incorporating the reticulocyte index into the PLASMIC score and validating it on TTP patients to increase its specificity without compromising its sensitivity.Future studies are needed to validate the diagnostic value of these laboratory abnormalities in distinguishing cobalamin-deficient thrombotic microangiopathy from TTP.

FIGURE 1 :
FIGURE 1: Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart of the selection process.

TABLE 3 : Distribution of the demographic and laboratory markers of patients with cobalamin- deficient thrombotic microangiopathy.
LDH = lactate dehydrogenase; WBC = white blood cell count; Hb = hemoglobin; MCV = mean corpuscular volume; NA = not applicable