Idiopathic neutropenia after clonal and antigenic exclusion: A progesterone-dependent subtype Free

Chronic idiopathic neutropenia (CIN) is characterized by a persistently reduced absolute neutrophil count, typically <1.5×10⁹/L for ≥3 months, without identifiable infectious, nutritional, autoimmune, clonal, congenital, or drug-related causes. It most commonly affects adult women, carries a variable risk of infection, and is frequently managed expectantly in the absence of severe or recurrent infections.

An index case of CIN with irregular menses and normalization of counts during pregnancy prompted an institution-wide review of adult neutropenia. U[p front we excluded cases of known congenital and drug-induced neutropenia. Among 238 presumed CIN patients, 88 had large granular lymphocytic (LGL) leukemia–associated neutropenia, 63 had autoimmune neutropenia defined by the presence of anti-neutrophil antibodies, and 87 met criteria for idiopathic neutropenia. Within the presumptive CIN group, extended blood antigen screening identified 12 patients with a Duffy-null phenotype, who were excluded from further idiopathic analysis (final n=75). This included 10 African American, 1 Caucasian, and 1 Asian patient. Extended blood-group profiling (Kidd, Colton, Lutheran, Dombrock, LW, ABO) showed no significant deviation from population frequencies.

In the remaining non-Duffy CIN patients, remarkably 54/75 were female with a mean age of 45±16 years. At presentation, mean WBC was 2.84±0.58×10⁹/L and ANC was 0.92±0.39×10⁹/L, Hgb was 13.5±1.2g/dL and platelets were 229±83×10⁹/L. Antinuclear antibodies were assessed in 73 patients, with 63 negative and 10 positive, predominantly speckled (66%) but rheumatologic consultation did not yield systemic autoimmune diagnoses. Hypothyroidism was noted in two CIN cases. Irregular menses were reported in 50% of female CIN patients with documented histories, and among those, 80% exhibited higher or normal neutrophil counts during gestation. Physiologically, pregnancy is a progesterone-high state associated with neutrophilia and physiologic leukocytosis; in addition, progesterone can dampen cytotoxic T-cell activity and inflammatory signaling while supporting marrow niche function. Furthermore, progesterone binds PR on marrow stromal cells and can upregulate CSF3 (G-CSF) and possibly other hematopoietic growth factors, thus regulating granulopoiesis. By contrast, anovulatory or irregular cycles often reflect luteal progesterone deficiency, which may predispose susceptible patients to lower ANC prompting us to formulate a theory that excess of CIN in females may be due to a progesterone-responsive CIN subtype. From our cohort, there were no patients on progesterone-supplement to evaluate if there would be responsiveness secondary to its utilization. To further support this theory we turned to metanalytic resources. TriNetX¹allowed us search and identify women receiving exogenous progesterone versus a control receiving non-hormonal contraceptives and assign to them a corresponding ANC. When we compared ANC in 1:1 greedy propensity-score matching to control for covariates (demographics, BMI, and disease confounders e.g., malignancy). balance between comparator groups was confirmed by standardized mean differences <0.10. After matching (n=18,561 per arm), the exogenous progesterone group had a significantly higher neutrophil count compared to non-hormonal contraception (1.9±3.7 vs 1.5±1.7; t=3.5, p=.0004). The cohort age range was similar to our patient population 44 ±19.

Our observations motivate prospective evaluation of progesterone-high states as potential modifiers of ANC in otherwise idiopathic cases and particularly refractory cases Cycle-synchronized CBC with paired progesterone and estradiol measurements, together with controlled progesterone augmentation trials, can quantify ANC changes and clinical outcomes in this subset.

We thank TriNetX and all participants for their contribution, without whom this research would not have been possible. References

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