Etiology and clinico-hematological profile of pancytopenia: experience of a Mexican Tertiary Care Center and review of the literature.

ABSTRACT Background: Pancytopenia is a frequent entity in clinical practice as a feature of a myriad of conditions, ranging from benign to malignant diseases. Since the cause of pancytopenia depends on environmental factors, it is important to know the common etiologies of pancytopenia, however, few studies address this. Objectives: To identify the etiology of pancytopenia in our population and compare them with what is reported elsewhere. Methods: We conducted an observational study of patients with pancytopenia in a Mexican Tertiary Care Center. Clinical, hematological and bone marrow studies were performed in all patients. Results: Of 109 cases included, the mean age at diagnosis was 49.4 years, with a slightly higher female incidence (53.2%). The most common causes of pancytopenia were: MDS (20.2%), megaloblastic anemia (18.3%) and AML (12.8%). Discussion: We found a complex picture of pancytopenia in Mexico and compared it with what is reported elsewhere in the literature. Conclusion: The sociocultural context in which the patients develop helps narrowing the possible etiology of pancytopenia, and therefore hasten the diagnostic process. Of all the studies available, bone marrow aspiration seems the most useful.


Introduction
Pancytopenia is the reduction of all three cellular elements of peripheral blood, leading to anemia, leukopenia and thrombocytopenia, and it is a clinicohematological entity commonly encountered in clinical practice as a feature of a myriad of diseases, ranging from non-malignant conditions, such as drug-induced pancytopenia, infections or nutritional deficiencies, to malignant neoplasms, either primary hematological malignancies or non-hematological metastatic malignancies. Considering that both treatment and prognosis depend on the cause of pancytopenia, it is essential to reach a definitive diagnosis as soon as possible [1][2][3].
Since the development of pancytopenia and its primary cause depend, among other things, on environmental factors [4,5], it is important to keep them in mind while studying a patient with pancytopenia, however, there are few reports about its epidemiology, specially in our population. Therefore, we decided to study the etiology of pancytopenia in a tertiary hospital, and then, compare our data with studies of pancytopenia worldwide. In this work, we report the first series of adult patients with pancytopenia in our country.

Methods
Patients admitted to the hospital with pancytopenia defined as Hemoglobin ≤13.5 g/dL in males or ≤11.5 g/dL in females, leukocytes ≤3.5 × 10 9 /L or neutrophils ≤1.5 × 10 9 /L and platelets ≤135 × 10 9 /L [6], from January 2007 to December 2011, were studied. The inclusion criteria were: (1) age >15 years old, (2) presence of pancytopenia, as defined above, (3) written consent for participation in the study. The exclusion criteria were: (1) patients with previously diagnosed pancytopenia, (2) patients in whom a final diagnosis could not be reached, (3) patients with incomplete medical records, (4) patients with previously known HIV infection. A complete clinical history, medical examination, a full blood count and bone marrow aspiration and/or biopsy were performed at the start of the study. When needed, additional diagnostic studies were performed. All data were analyzed using R Studio and Prism6.

Results
Of the 109 patients included, 58 were female (53.2%) and 51 were male (46.8%) with a mean age at diagnosis of 49.4  years. Clinically, more than 80% of patients presented with symptoms of anemia, pallor (82.6%) and weakness (81.7%) being the most frequent; and almost half had some kind of bleeding, being ecchymosis (29.4%) and petechiae (17.4%) the most common. Only 23 patients presented with fever and an infection could be documented in 20 cases.
The final diagnosis of pancytopenia was made with bone marrow aspirate analysis in 58 cases (53.2%), with bone marrow biopsy in 19 (17.4%) and bone marrow immunophenotyping in 14 patients (12.8%). In the remaining cases, other complementary studies were performed to achieve a diagnosis.

Discussion
Pancytopenia is the clinical triad of anemia, thrombocytopenia and leukopenia, and can be caused by a myriad of conditions. In our population, the clinical presentation of pancytopenia was marked by signs and symptoms of red blood cell and platelet deficiencies, while infections were limited. The most useful single study that aided the diagnostic process, in our series, was the bone marrow aspirate, allowing a final diagnosis in more than half of the patients included. In the rest of the cases, further diagnostic studies such as bone marrow biopsy and immunophenotyping were necessary, reaching a diagnosis in 83.4% of pancytopenia cases. This is similar to what is reported elsewhere [1,7].
We did not find significant differences in age distribution or peripheral blood cell counts that could help discriminate between benign and malignant pathologies, however, for patients with megaloblastic anemia due to either vitamin deficiency or pernicious anemia, we found a male to female ratio of 4:1 for vitamin deficiency megaloblastosis, which reversed to 1:4 for pernicious anemia [8,9]. Additionally, hypersplenism as a cause of pancytopenia was far more common in men than women, with a ratio of 1:5. Nonetheless, portal hypertension was present only in 2/10 female patients.
Regarding megaloblastic anemia, both folate but specially vitamin B12 deficiency is more common than previously thought, and several factors could be implicated, including the diminished absorption of B12 in older adults and the fact that depleting this vitamin's liver deposits is not as lengthy as described before [27,28]. This helps explain how countries like Mexico and Argentina, with an average supply of protein of animal origin of more than 40 g/capita/ day still have a high incidence of megaloblastic anemia as a cause of pancytopenia [29], although this was rare for developed nations.
This suggests that B12 deficiency could be the main cause of megaloblastic anemia in developing countries, as supported by a paper published in 2014 in an Indian population in which the authors found that most cases of macrocytic anemia were attributed to B12 deficiency, while almost 50% of cases with either microcytic or normocytic anemia were accompanied with cyanocobalamin deficiency [30]. Additionally, a relative excess of folic acid in comparison to B12 seems to detonate a more severe neurological and psychiatric symptoms, therefore, accurate diagnosis is important [27,30]. Moreover, B12 deficiency could likely be nutritional, since a study [31] demonstrated that only 3.9% of patients with macrocytosis had parietal cell autoantibodies. Nonetheless, a study found no clear correlation between vitamin levels, either folate or cobalamin, and the severity of anemia. This suggests that other factors influence its development and strain the need of performing further research in this topic [32].
With reference to hematological malignancies as a cause of pancytopenia, according to GLOBOCAN [46] of the World Health Organization, there is a higher overall age-standardized rate of cancer in more developed countries versus developing countries. This is true for Hodgkin's lymphoma (2.1 vs 0.6), multiple myeloma (2.7 vs 0.9), leukemia (7.2 vs 3.8) and non-Hodgkin's lymphoma (8.6 vs 3.6). This is similar to what we found in our review, since countries with a high gross domestic product (GDP), such as USA and France, where almost 50% of all adult cases with pancytopenia were due to hematological malignancies; furthermore, in our country, hematological malignancies comprised overall more than 40% of all cases of pancytopenia, suggesting possible similarities between these environments. Theories behind these findings include a diminished natural selection, effects of diet, the prevalence of obesity and overfeeding, and more; all which are discussed elsewhere [33][34][35]37]. Furthermore, although pancytopenia as a presentation of multiple myeloma and both Hodgkin and non-Hodgkin's lymphoma is not common in developed nations, there were cases both in our series and other developing countries [17,18]. In a report of a Mexican cohort of MM patients, 88% were on ISS stages II or III, suggesting an overall more advanced stage at presentation [38]. Additionally, a study by Perry et al. found that developing regions had a larger rate of high-grade B-cell lymphomas compared to developed countries (59.6% vs 39.2%, respectively) [39]. These disparities may be due to several reasons, including variations in tumor biology, delayed referral or diminished access to health care institutions; to fully explain this difference, further studies are needed.
As expected, malaria was a common cause of pancytopenia only in countries with a high incidence, according to data from the WHO Malaria Observatory and the WHO Malaria report, as are the cases of Yemen and Ivory Coast [36].
There was a higher incidence of pancytopenia due to AA in Asian countries compared to the rest of the world. In our country, AA as a cause of pancytopenia was not common, since it was the final diagnosis in only 11 patients. This is in accord to what is reported internationally, since AA is two to three times more common in Asian populations compared to North America and Europe, with an estimated incidence ranging from 3.9 to 7 per million [40,41]. In this regard, although the reports by the International Agranulocytosis and Aplastic Anemia Study Group did had a higher incidence of AA as a cause of pancytopenia, it is important to take into account that one of their criteria for inclusion was the suspicion of AA as a cause of pancytopenia, therefore, this data should be regarded with caution, especially since other studies from Europe have not arrived to the same results [7,19,41]. The reasons behind this disparity have been discussed elsewhere [42][43][44][45].
Overall, the data gathered support a complex picture for pancytopenia in our country, since both benign nutritional deficiencies and malignant hematological neoplasms were common in our population.

Conclusion
In studying a patient with pancytopenia, a good clinical correlation is of utmost importance to evaluate each specific case and plan for further evaluations. In this context, the most useful single study is the bone marrow aspirate. Nonetheless, with an extensive differential diagnosis, it is necessary to take into account the environmental factors that might suggest or narrow the possible etiologies to hasten the diagnostic process. It is therefore essential to study not only the patients but their sociocultural context. Taking this into account, studying the epidemiology of pancytopenia worldwide could help directing the diagnostic work up, and by this, hastening treatment and improving the prognosis.

Disclosure statement
No potential conflict of interest was reported by the authors.