Platelet function disorders are a heterogeneous group of inherited bleeding defects with bleeding severity ranging from mild to severe. While some patients may be asymptomatic, most present with ecchymosis, epistaxis, HMB or excessive bleeding associated with surgical procedures or trauma. The present retrospective study includes the largest reported series on adolescents that clinically manifest HMB due to platelet function disorders (n=43). The study methodically evaluates in this population subgroup various clinical and laboratory characteristics not previously examined. Data from the study offer novel insights into the early natural history of the disorder that will assist in its characterization as well as earlier identification.
Observations from the present study intriguingly suggest that adolescents with PFDs that manifest HMB after menarche represent a clinically distinct phenotype from similarly affected teenagers that do not develop HMB after pubertal transition. Indeed the possibility that intra- and intergroup differences exist at the genomic or proteomic levels and these differences influence variable phenotypic bleeding manifestations is supported by the finding of a significantly higher incidence of the δ-SPD (74%) in adolescents with HMB when compared with non-HMB teenagers (P<.007).
The incidence of HMB was considerable among adolescents with documented PFDs. It was the most common bleeding symptom, manifesting in over two-thirds (68%) of young females affected with PFDs. Both the (mean) age-at-PFD diagnosis and the presenting symptomatology differed between the 2 groups. Young girls that developed HMB after menarche were significantly older when they were diagnosed with a PFD—by 3.6yrs—when compared with non-HMB teens (P<.01). Indeed, a significant majority (86%) were diagnosed with a PFD at or after the menarche based on HMB symptoms, while 14% were rendered a PFD diagnosis prior to the menarche based on associated bleeding, e.g., epistaxis, ecchymosis, etc. (P<.01) Overall, only 30% of patients diagnosed with a PFD prior to menarche subsequently manifested HMB after pubertal transition, and all had the δ-SPD, while a large majority (70%) did not develop HMB after menarche (42mo median follow-up).
Significant differences between age-at-PFD diagnoses may in part reflect bleeding severity. Individuals with severe bleeding symptoms often present early in childhood, suggesting patients that did not manifest HMB after menarche presented with more severe bleeding that led to earlier evaluation and diagnosis
. Some may have had family members with positive bleeding histories, prompting earlier evaluation. However, owing to the heterogeneity of PFDs, it is possible that some may not have manifested as severe bleeding symptoms as other patients with de novo PFD diagnoses, but without positive familial bleeding histories. Additionally, our HMB teens shared a similar high prevalence of family bleeding tendencies and yet were diagnosed with a PFD at an older age. Hemostatic challenges did not appear to influence earlier PFD diagnoses as evidenced by similar intergroup surgery-associated bleeding histories, particularly childhood tonsillectomies and adenoidectomies. Treatment regimens, such as desmopressin acetate, tranexamic acid, etc., may have prevented HMB. However, therapeutic intervention does not explain the existence in our study of a subset of young girls diagnosed with a PFD prior to menarche (14%) that developed HMB after transitioning into puberty. Indeed, similar findings were recently reported in a study by Chi et al. in which the diagnosis of a bleeding disorder was known in 64% of young females prior to their presentation with menorrhagia, yet they developed HMB despite instruction to take tranexamic acid when menses began
The long (mean) 1.8-year interval between menarche-to-HMB onset was at variance with prior studies on menorrhagia that reported HMB occurring predominately at or within the first year of menarche in patients with bleeding disorders
[4, 6, 7, 9]. Indeed, Chi et al. reported HMB onset occurred at menarche in 90% of adolescents affected with bleeding disorders
. Adolescents with PFDs that clinically manifested HMB have not been exclusively analyzed until the present report. It is possible that differences in the menarche-to-HMB interval may be related in part to prior studies intermixing data from PFD patients with data from subjects affected with disparate bleeding disorders, thus obscuring the actual temporal relationship
[4, 5, 7, 14]. Of interest, PFD adolescents that clinically manifested HMB were not anemic. For these patients, the menarche was a recent event with the PFD diagnosis rendered close to the menstruation onset. This may have aided in earlier treatment initiation that may have in turn mitigated heavy bleeding and subsequent anemia.
A substantial number of adolescents with PFDs, 70-76%, had blood type O, intriguingly paralleling the 77% type O frequency reported for VWD, type I individuals
[29, 30]. Indeed, the high blood type O phenotypic frequency was an unexpected finding and to our knowledge has not been previously reported. When examined in the context of a comparable U.S. population, blood group O occurred in our PFD adolescents significantly more frequently and types A and B, less frequently (P<.037)
[21, 22]. Prior studies on menorrhagia have reported type O blood occurring in 44-59% of their patients, paralleling national norm frequencies, despite their inclusion of numerous VWD females
[8, 9, 11, 12]. Blood type O individuals have VWF levels approximately 25% lower than non-type O individuals. Our patients had normal ABO-adjusted VWF testing with only one patient, with combined PFD-VWD, type I showing VWF studies diagnostic for VWD diagnosis. The mechanism for the preponderance of blood group O, in the absence of VWD in our PFD adolescents is unknown
[29, 30]. Indeed, mechanisms influencing blood group O on plasma VWF levels are elusive. Variable VWF carbohydrate structures have been associated with lowered VWF levels in blood group O individuals. Additionally, blood group O individuals have significantly higher rates of VWF proteolysis by the metalloproteinase, a disintegrin and metalloproteinase with thrombospondin motif, member 13 (ADAMTS13) when compared with non-O individuals
. Genetic differences in ADAMTS13 levels may also influence VWF clearance in type O blood groups. Lower VWF levels (not diagnostic for VWD) as reported in blood type O individuals, combined with functional platelet defects, particularly the δ-SPD, may represent an additional variable adversely affecting hemostasis that renders PFD-blood type O individuals more vulnerable to bleeding than PFD patients expressing A, B blood types.
The significant association between adolescents with HMB and PFD, particularly the δ-SPD, suggests that blood type O may be a useful identifier for these disorders and may assist clinicians in stratifying patients for additional studies. Certainly, blood typing is not intended to serve as a screening test for bleeding disorders. However, if blood typing has been performed, data from our study indicate adolescents presenting with HMB that express blood type O, have normal coagulation profiles and ABO-adjusted VWF tests for VWD, and platelet aggregation studies that are either normal or impaired by a single agonist defect may benefit from additional EM studies to exclude the δ-SPD. Without a definitive diagnosis, such as that offered by EM, many patients with this disorder may go undetected.
Prior reports and data from our study indicate that standard platelet screening by closure times (PFA system) and LTA have moderate sensitivity in detecting and diagnosing PFDs, particularly the δ-SPD
[15, 26, 32–36]. The Hayward et al. 2006 report of a survey on published literature regarding PFA efficacy concluded that the test lacked adequate sensitivity in screening for platelet disorders
. Philipps and coworkers studied the utility of closure times (PFA) and bleeding times in screening for bleeding disorders in women with HMB. Their data indicated the PFA had a sensitivity of 23%, specificity of 92%, positive predictive value of 75% and a negative predictive value of 52% in women with PFDs
. Cattaneo et al. studied closure time (PFA system) and bleeding time effectiveness in patients with δ-SPDs and platelet secretion defects and concluded that both tests performed with similarly low sensitivity
. Data from these reports supports our finding of high false negative closure times.
Platelet LTA, considered the “gold standard” for diagnosing PFDs, has well-known limitations
[26, 37]. The issue of whether single agonist-induced aggregation defects can accurately detect a PFD is a potential limitation. Most patients with PFDs, 29.7% - 30.3%, in 2 prior studies on HMB had single agonist defects identified by platelet aggregation studies. In our study, the majority (45.7%) of HMB patients had multiple agonist-induced aggregation defects, while only 14.3% had a single agonist abnormality and our non-HMB group showed similar testing results. Hayward et al. reported that reduced maximal aggregation with >1 agonists significantly increases PFD detection
[12, 15, 38]. Miller et al. recently addressed the criterion of >1 agonist defects and the subject of multiple statistical comparisons used in platelet function testing. The authors noted that had the >1 agonist criterion been applied in their study, 30.3% of patients would have been excluded, as would those patients affected with a single platelet receptor defect to one agonist (e.g., collagen, ADP)
. In our study, 14.3% of HMB patients with single agonist defects would have been similarly excluded, all of whom were diagnosed with the δ-SPD by EM. Indeed, these 5 patients with the following LTA single agonist defects: 0.5 μM ADP (3); 60 μM epinephrine (1); and 0.5 mmol/L AA (1) all had significantly reduced platelet δ-granules on EM. Miller et al. appropriately cautioned against rendering a PFD diagnosis on the basis of a single test
. However, some patients with the δ-SPD have single agonist aggregation defects, as identified in 14.3% in our study, as well as normal aggregation studies. Nieuwenhuis et al. reported on 106 patients with platelet disorders with 25% having normal platelet aggregation studies and all were subsequently diagnosed with the “SPD” by total platelet ADP and serotonin testing
. Israels et al. similarly reported on a subset of 15 patients with normal aggregation studies subsequently diagnosed with “platelet storage pool deficiency” by EM and ATP release testing
. These studies parallel our findings. Indeed, the δ-SPD diagnosis would have been missed in an additional 25.6% and 10% of our HMB and non-HMB teenagers, respectively, that had normal standard platelet function studies (closure times by PFA; LTA) and for whom EM studies revealed significantly reduced platelet δ-granule numbers.
EM may be indicated in some cases as a confirmatory method for detecting diminished granule numbers
[23–26, 34]. Although not widely available, other diagnostic studies for the δ-SPD, such as flow cytometry of mepacrine uptake, are similarly not widely available. Clinical judgment should be rendered; as previously stated, data from our study indicate that young girls with HMB, normal coagulation profiles and ABO-adjusted VWF tests for VWD, blood type O, and normal or single agonist defects on platelet function studies, would be excellent candidates for EM studies for detecting the δ-SPD. EM studies are done at a number of centers. Excellent distinctions between normal and diminished δ-granule numbers have been reported among those institutions included in a recent study by Hayward et al.
Limitations to the study include those common to retrospective reports. There was an absence of an adolescent control group with unexplained HMB after exclusion of all non-hematologic etiologies. We sought in part to define the clinical profile of PFD adolescents at presentation and no attempts were made to correct for PBAC changes over time and after treatment. Sanitary products were not standardized and this is an infrequent limitation
[4–8, 11–15]. A small minority of HMB patients did not have platelet LTA results recorded, with only observed data used in the analyses and this is an infrequent occurrence
[4, 5]. The potential for selection bias in our specialist-referred patient population and cases sent for EM cannot be excluded. A potential confounder is whether timing of platelet samples sent for EM either during or shortly after a hemostatic challenge affected δ-granules numbers. Exhausted platelet granules would be expected to adversely influence platelet aggregation studies, yet 40% of adolescents with reduced δ-granule numbers on EM had normal platelet aggregation studies. Despite these limitations, detailed clinical and laboratory data obtained from the study has assisted in defining the characteristics of adolescents with platelet dysfunction-associated HMB that have never before been reported on. Data from the study provides a foundation for future longitudinal cohort studies. Additionally, these data will aid clinicians in earlier diagnosis of the disorder and will alert them to select additional platelet testing, such as EM, particularly in the presence of normal standard platelet function studies.