Autoimmune neutropenia (AIN) is a benign hematologic disorder that typically affects children under 5 years of age and spontaneously resolves within 3 years from the onset.1 However, some atypical forms occur later in life, have a lower resolution rate, and may be associated with systemic autoimmune phenomena.2 In any case, the main mechanism of neutrophil reduction seems to be related to the presence of antibodies that cause peripheral cell destruction by binding to membrane antigens such as IgG type 3b Fc receptor (FcγIIIb receptor).3 Some alternative mechanisms involving cellular immunity and Treg cells have been proposed.3 However, the pathogenesis of AIN is still not entirely clear.

AIN is usually asymptomatic, and the frequency of severe infections is very low.1,2 It has already been shown that viral infections do not complicate the clinical course of the disease.4 However, Coronavirus disease 2019 (COVID-19), which usually presents with mild symptoms in children,5 has been associated with neutropenia in pediatric age.6 Therefore, the occurrence of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infection in patients with AIN is of great concern to families and physicians. Clinical reports of SARS-CoV-2 infection in children with AIN are currently not available in the medical literature.

Herein, we present the retrospective clinical description of SARS-CoV-2 infection in a homogeneous cohort of patients with AIN. In addition, we studied the trend of absolute neutrophil count (ANC) and absolute lymphocyte count (ALC) after infection and compared it with the median of values before SARS-CoV-2 infection.

PATIENTS AND METHODS

We retrospectively studied the medical charts of patients followed for AIN in our tertiary referral hospital in the period between April 1, 2020, and December 1, 2022.

Patients with a reported SARS-CoV-2 infection were included.

The diagnosis of AIN has been established based on the presence of chronic neutropenia with at least one positive anti-neutrophil antibody (Granulocyte immunofluorescence test) and the exclusion of infectious, drug-induced and congenital causes. The resolution of neutropenia was determined by the finding of at least 3 consecutive ANCs in the normal range for age. The presence of systemic immune dysregulation diseases (eg, systemic lupus erythematosus) or hematologic diseases (malignancy and bone marrow failure) was excluded due to a lack of clinical criteria and negativity of laboratory tests. In some selected patients, the diagnosis was further supported by bone marrow aspirate evaluation and/or genetic examination by clinical exome. Superinfections were excluded by blood cultures and microbiological tests.

We analyzed clinical data (signs and symptoms, length and treatment of AIN, comorbidities, previous anti-SARS-CoV-2 vaccination, co-infections and treatments) and laboratory data, including ANC, ALC and C-reactive protein values, for the period of SARS-CoV-2 infection.

To investigate the impact of the infection on the natural history of the disease, ANC and ALC values for the entire preinfection period and their postinfection values were collected. ANC values with concomitant elevation of C-reactive protein, during Granulocyte-Colony Stimulating Factor therapy or infectious episodes other than SARS-CoV-2 infection were excluded.

Data were collected according to the Helsinki Declaration of Principles.

Statistical Analyses

Statistical analyses were performed using Stata version 13 software and GraphPad Prism 6 (GraphPad Software, Inc., San Diego, CA). Continuous variables were presented as the median and interquartile range (IQR) and evaluated using the Mann-Whitney U test. The Normality test (D’Agostino and Pearson) was used to test the normal distribution of the data. Wilcoxon matched-pairs signed rank test was used to compare pre- and post-infection values. To analyze the correlation between the postinfection ANC and ALC values, we used Pearson’s correlation coefficient.

RESULTS

Of a total of 53 patients evaluated for AIN during the period analyzed, 24 episodes of SARS-CoV-2 infection were observed in 22 patients. Two patients had 2 infectious episodes. The most observed symptom of SARS-CoV-2 infection was fever (18/24). Upper respiratory (10/24) and gastrointestinal involvement (6/24) were less frequent. Six out of 22 patients were hospitalized. Seven patients received antibiotic therapy in the course of the SARS-CoV-2 infection. Patient 15 received piperacillin/tazobactam in both infection episodes due to the presence of erythematous skin lesions and low ANC values. None of the patients in the entire cohort was treated with antiviral drugs or monoclonal antibodies.

Because of the retrospective nature of this study and the isolation rules for nonhospitalized SARS-CoV-2 positive patients, Complete blood count values were obtained in only 8 cases in the course of SARS-CoV-2 infection (Table 1). Lymphopenia was observed in 5 out of 8 cases: patients 15 (in both infections), 16, 19 and 22.

TABLE 1.  - Characteristics of the Cohort of AIN Patients With SARS-CoV-2 Infection Patient Age (Months)/Sex AIN Length (Months) at the Time of Infection AIN Treatment Comorbidities Previous Anti-SARS-CoV-2 Vaccination (doses) Fever Other Symptoms CRP (mg/dl; Max Value) ANC (Median, IQR) Hospitalization Treatments 1 21/M 17 No Renal pyelectasis No Yes Cough - - No No 2 25/M 12 No Sideropenic anemia No No No - - No No 3 170/M 6 No No No No Pharyngitis - - No No 4 29/F 8 No No No Yes No - - No No 5 17/F 8 No Vesicoureteral reflux No No No - - No No 6 125/F 73 No No Yes (2) Yes Aphtosis, headache - - No No 7 38/F 33 GCSF No No Yes No 0.75 1030 No Clarithromycin 8 130/M 4 No No No Yes Rhinitis, diarrhea - - No Amoxicillin/clavulanate 9 47/F 3.2 No No No Yes EBV coinfection -- - No No 10 21/F 14 No No No Yes No - - No No 11 73/M 42 No IgA deficiency No Yes No - - No No 12 111/M 81 No Tourette Syndrome; asthmatic bronchitis No Yes Arthralgia, skin rash, abdominal pain - - No No 13 33/F 24 No No No Yes No - - No No 14 39/F 27 No G6PDH deficiency No Yes Vomiting, diarrhea 3.88 1440 (1050–3760) Yes Piperacillin/tazobactam 15 59/F 30 No No No Yes Pharyngitis, abdominal pain, conjunctival hyeremia, skin pustules 0.76 130 (110–190) Yes Piperacillin/tazobactam 15 67/F 38 No No No Yes Pharyngitis, abdominal pain, skin pustules 1.82 190 (180–230) Yes Piperacillin/tazobactam 16 8/F 0 No No No Yes Laryngospasm 2.34 305 (190–597,5) Yes Aerosolic steroids, amoxicillin/clavulanate 17 6/F 0 No No No Yes Skin rash 0.31 300 (275–530) Yes Ibuprophen, amoxicillin/clavulanate 18 124/F 96 No Cyclical vomiting syndrome No Yes Pharyngitis - - No No 18 136/F 108 No No No Yes Cough, abdominal pain - - No No 19 19/F 11 No No No Yes Rhinitis, cough 0.3 805 (705–1287,5) Yes No 20 78/M 51 No No Yes (2) Yes No - - No No 21 290/M 73 No ITP treated with Eltrombopag Yes (2) No Rhinitis - - No No 22 22/F 12.5 No Febrile seizures No Yes Febrile seizures - 485 (292–677) Yes Ceftriaxone

AIN indicates autoimmune neutropenia; ANC, absolute neutrophils count; CRP, C-reactive protein; EBV, Epstein-Barr Virus; GCSF, Granulocyte-Colony Stimulating Factor; G6PDH, glucose 6 phosphate dehydrogenase; ITP, immune thrombocytopenia; IQR, interquartile range.

CRP cutoff value: 0.5 mg/dl; -, not available.

At a median time of 43.5 days after recovery from SARS-CoV-2 infection, an increase in ANC values was found in 15/18 (83%) evaluable patients compared with the median ANC values of the previous follow-up period. Only 1 patient (n. 12) showed a reduction in values from mild to moderate neutropenia.

Patients 3, 4,14 and 17 completely recovered from AIN at 4, 3, 5 and 13 months after infection, respectively.

Eleven out of 17 patients presented a reduction in lymphocyte values below 25° centile of the values at the previous follow-up (Table, Supplemental Digital Content 1, https://links.lww.com/INF/F250). Overall, a significant elevation of ANC values (P < 0.0006) and a reduction in lymphocyte postinfection levels (P < 0.0081) were observed compared with the preinfection period (Fig. 1). A negative correlation between lymphocyte and neutrophil values at postinfection control was observed (r = −0.32).

FIGURE 1.:

Comparison of ANC and ALC values pre- and post-SARS-CoV-2 infection. ALC, absolute lymphocyte count; ANC, absolute neutrophil count.

No difference in median length of AIN at the time of infection was observed for patients with ANC increased values and patients with stable or reduced values [17 (IQR, 8–42) and 24 (IQR, 11–51), respectively; P = 0.9].

DISCUSSION

Since the beginning of the pandemic, several studies have investigated the importance of hematological abnormalities during SARS-CoV-2 infection and its prognostic relevance. Neutropenia has seldom been described in adults with COVID-197 while it appears to be more common in children.6 Descriptions of the impact of SARS-COV-2 infection in patients with chronic neutropenia are anecdotal and limited to a few case reports, often reaching discordant conclusions.8,9

To the best of our knowledge, this is the first study showing the trend of SARS-CoV-2 infection in a homogeneous cohort of pediatric patients with AIN.

In all 24 cases reported, COVID-19 progressed with mild symptomatology. Fever was present in almost all patients, while respiratory symptoms were mild and affected only a small proportion of cases. No patients required intensive care, and the hospitalization rate was very low (27%). None of the patients in the entire cohort experienced bacterial superinfection except for minor skin lesions in 1 case who received empirical antibiotic therapy during hospitalization.

Overall, the clinical data collected during SARS-CoV-2 infection in our cohort allows us to conclude that COVID-19 has a rather benign course in patients with AIN in the absence of significant bacterial co-infections.

Interestingly, in 2 patients (16 and 17), AIN was diagnosed at the time of the SARS-CoV-2 infection, with the concomitant detection of neutrophil antibodies and the persistence of neutropenia for more than 3 months after the resolution of the infection. It is possible that the neutropenia was already preexisting at the time of the SARS-CoV-2 infection, at which it was incidentally found. However, it can be speculated that autoantibody production may have been triggered by SARS-CoV-2 itself. This is consistent with the literature, as some studies hypothesized that the onset of AIN may be secondary to viral infection.10 On the other hand, several studies have recently associated SARS-CoV-2 with the onset or recrudescence of autoimmune diseases.6

Regardless of the severity of COVID-19, retrospective analysis of preinfection and postinfection Complete blood counts revealed interesting changes.

Most patients showed improvement in postinfection ANC values. Overall, the increase in ANC at approximately 43 days from COVID-19 recovery was statistically significant compared with median values preceding the infection (Fig. 1). We speculate that this finding could be explained by the peculiar ability of SARS-CoV-2 to bring about immunological changes even for months after recovery.5 An altered phenotype of circulating leukocytes has been described up to 3 months after the onset of symptoms, even in patients who had a mild course of SARS-CoV-2 infection.5

Moreover, elevated levels of cytokines and chemokines (eg, CXCL10 and CCL19) have been demonstrated in children with mild or asymptomatic COVID-19, confirming the proinflammatory effect of SARS-CoV-2 infection that may lead to neutrophils peripheral recruitment.11

Interestingly, 1 patient in our cohort, suffering from immune thrombocytopenia (ITP) and AIN, shows a significant increase in both ANC and platelet values as well as an ALC reduction 36 days after SARS-CoV-2 infection (Table, Supplemental Digital Content 1, https://links.lww.com/INF/F250).

De la Cruz-Benito et al.12 proposed that reduced production of autoantibodies may underlie the significant improvement in platelet values after SARS-CoV-2 infection in a cohort of patients with ITP. Similar to AIN, the pathogenesis of ITP is based on peripheral platelet destruction mediated by autoantibodies.13 Therefore, a mechanism of reduced autoantibody production can be hypothesized to explain the paradoxical effect of ANC observed in our cohort of AIN.

The reason for the improvement in neutrophil values in the weeks following infection could lie in the alterations induced by COVID-19 on regulatory cell homeostasis and in lymphopenia itself, which could transiently reduce the production of autoantibodies responsible for the destruction of peripheral neutrophils.3,5 Finally, in patients with atypical autoimmune neutropenia (as defined in the recent literature2), SARS-CoV-2 infection also occurred in a mild form with a similar impact on ANC and ALC values. This retrospective study has many limitations. Although it is a homogeneous cohort, the number of patients is limited and the time of assessment of post-infection ANC values is variable.

Further prospective studies are needed to understand how SARS-CoV-2 infection may affect patients with AIN.

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