Postnatal cytomegalovirus infection and pulmonary vascular disease in extremely premature infants: A case series

Abstract

BACKGROUND:

Pulmonary vascular disease (PVD) is a major determinant of both morbidity and mortality in extremely low birth weight infants. It is biologically plausible that postnatal cytomegalovirus (pCMV) infection may lead to PVD in premature infants secondary to pneumonitis or via derangement of pulmonary vascular development directly through endothelial dysfunction. Uncertainty remains, however, regarding thresholds for intervention in premature infants with cardiorespiratory instability and presumed CMV infection likely secondary to the limited understanding of the natural history of the disease.

METHODS/RESULTS:

We describe four cases of premature infants with clinical and echocardiography features of PVD, in the setting of postnatally acquired CMV. All patients had atypical PVD trajectories, refractory to vasodilator treatment, which improved after initiation of CMV treatment.

CONCLUSION:

We highlight the need to consider postnatally acquired CMV infection in patients with PVD non-responsive to standard pulmonary vasodilator therapies or disease severity which is out of proportion of the usual clinical trajectory. Treatment of extremely premature infants with CMV-associated PVD may have positive impact on cardiorespiratory health, although duration of therapy remains uncertain.

1 Introduction

Cytomegalovirus (CMV) can cause perinatal and postnatal infection via exposure to infected maternal genital secretions or breastmilk or through iatrogenic exposure to blood products. Postnatal CMV (pCMV) typically occurs within the first postnatal months and is usually asymptomatic in term infants [1]. However, preterm infants are more frequently affected by symptomatic disease in the second or third postnatal month [2]. CMV infection is typically described as a sepsis-like syndrome with pneumonitis, colitis, hepatitis, bone marrow suppression, retinitis and meningoencephalitis [3 –5]. In addition, there is evidence of myocarditis, atherosclerosis, and coronary artery disease via endothelial dysfunction in pediatric and adult transplant patients [6, 7]. There is, however, limited understanding of the impact of CMV disease on pulmonary vascular development in either neonate, pediatric or adult populations [1]. Furthermore, while reports of early pulmonary hypertension (PH) in the setting of congenital CMV exist [8 –10], the relationship of postnatal acquired CMV to pulmonary vascular maldevelopment in preterm infants remains unknown. Preterm infants are at risk of developing pulmonary vascular disease (PVD) secondary to vascular pruning, abnormal vasculature, and increased vaso-reactivity [11]. It is biologically plausible that pCMV in premature infants may lead to PVD secondary to pneumonitis or via derangement of pulmonary vascular development directly through endothelial dysfunction.

In this report, we describe the illness natural history of a small case series of extremely premature infants with hypoxemic respiratory failure (HRF) and PVD which improved after treatment of CMV. PH represents the most severe form of PVD, which contributes to the late morbidity and mortality of infants with bronchopulmonary dysplasia (BPD) [12]. The key features of resistance mediated PH are increased pulmonary vascular resistance (PVR) which leads to high pulmonary artery pressure (PAP), right to left transductal or atrial level shunting, right ventricular (RV) dysfunction, and ultimately left ventricular (LV) dysfunction due to interventricular interaction [11]. In infants with CMV and PVD, it is biologically plausible that treating the underlying etiology, CMV, may improve pulmonary hemodynamics.

2 Case review

Four cases of infants with pCMV and echocardiography evidence of PVD admitted to the quaternary neonatal intensive care unit (NICU) at the University of Iowa Stead Family Children’s Hospital between November 2018 and February 2021, were reviewed.

2.1 Standardized Targeted Neonatal Echocardiography (TnECHO) approach in high-risk preterm infants

Routine TnECHO screening of preterm infants born at gestational age ≤30 weeks begins within the first postnatal week and continues through out NICU admission with the aim to facilitate timely detection of underlying cardiovascular pathology (Fig. 1). In addition to all planned screening assessments, the clinical team may request a hemodynamic consultation at any time. Comprehensive echocardiography assessment of PVD includes multiple objective measurements (Fig. 2). PVD was defined by the presence of echocardiography confirmed evidence of elevated PVR and/or PH (acute or chronic). We used a standardized definition of PH based on systolic eccentricity index (sEI) ≥1.3 [13, 14] and/or right ventricular systolic pressure (RVSP) greater than 30 mmHg + estimated right atrial pressure [15] and/or bidirectional or right to left patent ductus arteriosus (PDA) shunt. We used a standardized definition of elevated PVR according to pulmonary vascular resistance index (PVRi) > 4 or the presence of a mid-systolic notch, also referred to as the “flying W” [16].

Fig. 1

Screening Targeted Neonatal Echocardiography guidelines for infants less than 30 weeks gestation. Routine screening TnECHO is performed within the first 24 postnatal hours in infants born less than 27 weeks GA, and between postnatal day 4–7 in infants born between 27 and 29 weeks GA, to characterize underlying cardiovascular physiology. Continued TnECHO surveillance for chronic PH is again performed in all infants less than 30 weeks GA at the earlier of either 8 postnatal weeks or 36 weeks PMA to again facilitate timely detection. Repeat assessments occur at least every 3–4 weeks while the patient remains on oxygen (if the TnECHO is normal), or sooner if abnormalities are detected. All members of the Neonatal Hemodynamics team who acquire echocardiography information have completed at least basic TnECHO training and either had completed or were in the process of completing advanced training on the basis of American Society of Echocardiography in collaboration with the European Association of Echocardiography and the Association for European Pediatric Cardiologists guidelines [29]. All screening assessments were performed according to a standardized protocol that includes comprehensive imaging of intracardiac anatomy, biventricular function, outflow tract concordance and integrity, aortic arch anatomy, pulmonary vein location/flow, and transitional shunts [30]. TnEcho: Targeted neonatal echocardiography; cPH: chronic pulmonary hypertension; PVD: pulmonary vascular diease; GA: gestational age; PMA: post menstural age.

Fig. 2

Echocardiography assessment of pulmonary hemodynamics. (A) Systolic PAP can be estimated by measuring the peak velocity of tricuspid valve regurgitation (TR) with the use of the modified Bernoulli’s equation [11]. A tricuspid valve regurgitation jet of 30mmHg + right atrial pressure (RAp) is diagnostic of PH (B): Pulse wave doppler of bidirectional patent ductus arteriosus: assessment of the direction of transductal blood flow will indicate the relation between pulmonary and systemic pressures (C): Assessment of the alignment of the interventricular septum (IVS) in the parasternal short axis view above the level of the papillary muscles. Normally the septum bows into the right ventricle (circular-shaped LV), and with increasing right ventricular pressure, the IVS will flatten (D-shaped LV) and eventually bows resulting in a crescent-shaped LV [31]. Objectively, the degree of flattening of the IVS can be obtained by calculating the LV systolic eccentricity index (sEI), which is the ratio of LV dimension parallel and perpendicular to the septum, respectively [32]. Normative data suggest the sEI ratio to approximate 1 and sEI≥1.3 is indicative of pulmonary pressure values at least half systemic. Image on the left shows round septum with sEI < 1.3. Image on the right demonstrates flat septum with sEI > 1.3. (D): Patterns of pulmonary artery dopplers. Pulmonary artery acceleration time (PAAT) to right ventricular ejection time (RVET) ratio or pulmonary vascular resistance index (PVRi) has been validated as a feasible and reproducible, non-invasive echocardiography imaging marker, for detection of PVD. Image on the left shows elevated PVRi (RVET:PAAT > 4). Image on the right shows notched PVRi.

2.2 Clinical data

Demographic and clinical characteristics of each patient are summarized in Table 1. All cases presented with respiratory failure and PVD. CMV testing was prompted by illness severity which was considered by the clinician to be out of proportion to the typical NICU course and/or the lack of clinical improvement with standard medical treatments. Viral diagnosis was confirmed by polymerase chain reaction (PCR) of either plasma or whole blood. None of these cases demonstrated hepatic involvement. One patient was noted to have thrombocytopenia (49,000 K/mm³) and while none were noted to have retinitis, one patient had detectable CMV by PCR of cerebral spinal fluid (CSF). In all four cases there was interval improvement in clinical (Table 2) and echocardiography (Table 3) status after treatment with anti-viral therapy. None of the four infants developed significant neutropenia or alanine aminotransferase elevation during their inpatient treatment.

Table 1
Demographic information and clinical characteristics of the cases

Case 1 Case 2 Case 3 Case 4

Gestational age at birth 25 weeks 25 weeks + 4 days 24 weeks + 1 day 26 weeks

Birth weight (grams) 700 640 609 762

Sex Female Male Male Female

Age at presentation 42 weeks + 1 day 31 weeks + 5 days 34 weeks + 1 days 54 weeks + 1 day

Age at presentation (day of life) 120 43 70 197

Presenting clinical diagnosis Respiratory failure, Respiratory failure, Respiratory failure, Respiratory failure,

echo confirmed echo confirmed echo confirmed echo confirmed

pulmonary vascular pulmonary vascular pulmonary vascular pulmonary vascular

disease disease disease disease

Fever No No No No

Bone marrow involvement No No Thrombocytopenia No

(lowest level: 49 K/mm³)

Liver involvement (hepatitis) No No No No

Retinitis No No No No

	Case 1	Case 2	Case 3	Case 4
Gestational age at birth	25 weeks	25 weeks + 4 days	24 weeks + 1 day	26 weeks
Birth weight (grams)	700	640	609	762
Sex	Female	Male	Male	Female
Age at presentation	42 weeks + 1 day	31 weeks + 5 days	34 weeks + 1 days	54 weeks + 1 day
Age at presentation (day of life)	120	43	70	197
Presenting clinical diagnosis	Respiratory failure,	Respiratory failure,	Respiratory failure,	Respiratory failure,
	echo confirmed	echo confirmed	echo confirmed	echo confirmed
	pulmonary vascular	pulmonary vascular	pulmonary vascular	pulmonary vascular
	disease	disease	disease	disease
Fever	No	No	No	No
Bone marrow involvement	No	No	Thrombocytopenia	No
			(lowest level: 49 K/mm³)
Liver involvement (hepatitis)	No	No	No	No
Retinitis	No	No	No	No

Table 2

Clinical course before and after treatment of cytomegalovirus

	Respiratory	Oxygen	Respiratory medications ¥	Pulmonary
	support	requirement		hypertension
				medications
Case 1	NIV NAVA	0.45	Hydrochlorothiazide, fluticasone inhaler	iNO
Before CMV treatment	Level 1.2, PEEP 12		prednisolone, and azithromycin	Inhaled Epoprostenol
	cmH₂0
After CMV treatment	Nasal CPAP	0.3	Chlorothiazide and fluticasone inhaler,	Sildenafil
	8 cmH₂0
Case 2	HFJV	0.5	Chlorothiazide, fluticasone inhaler,	iNO
Before CMV treatment	MAP 13		and theophylline
After CMV treatment	HFJV	0.3	Chlorothiazide, fluticasone inhaler,	None
	MAP 11 cmH₂0		and theophylline
Case 3	SIMV	0.75	Chlorothiazide, fluticasone inhaler,	iNO
Before CMV treatment	MAP 15 cmH₂0		prednisolone, and azithromycin
After CMV treatment	Nasal CPAP	0.6	Chlorothiazide, fluticasone inhaler,	None
	12 cmH₂0		and azithromycin
Case 4	Nasal CPAP	0.75	Fluticasone inhaler, prednisolone,	iNO 20 ppm
Before CMV treatment	8 cmH₂0		and azithromycin
After CMV treatment	Nasal CPAP	0.5	Fluticasone inhaler, prednisolone,	iNO 10 ppm
	6 cmH₂0		and azithromycin

¥ Standard protocol dosing for respiratory medications: hydrochlorothiazide: 1.5 mg/kg BID PO; chlorothiazide: 10 mg/kg twice daily PO; fluticasone inhaler: 44 mcg 2 puff twice daily; prednisolone course: 1 mg/kg twice daily for 10 doses, followed by 1 mg/kg daily for 10 doses, followed by 1 mg/kg every other day for 10 doses, and finally 0.5 mg/kg every 48 hours for 10 doses; azithromycin: 5 mg/kg twice daily PO for one week followed by 5 mg/kg daily PO for 5 weeks. NIV NAVA: neurally adjusted ventilator assist iNO: inhaled nitric oxide, CPAP: continuous positive airway pressure, HFJV: high frequency jet ventilation, MAP: mean airway pressure, SIMV: synchronized intermittent mechanical ventilation.

Table 3

Echocardiography findings before and after treatment for cytomegalovirus

	LV	LV	Pulmonary	RV systolic	Pulmonary Hemodynamics	RV	PVR
	systolic	diastolic	vein flow	function		dilation
	function	function
Case 1	Normal	Normal	Normal	Normal	Moderate PH:	Normal	Notched
Before CMV treatment					RVSp > 60 mmHg + RAP
After CMV treatment	Normal	Normal	Normal	Normal	No PH:	Normal	Normal (3.1)
					RVSp > 28 mmHg + RAP
Case 2	Normal	Normal	Normal	Normal	Systemic level PH:	Normal	Notched
Before CMV treatment					bidirectional PDA
					Notched PA Doppler
After CMV treatment	Normal	Normal	Normal	Normal	Resolution of PH	Normal	Borderline
					with left to right PDA		elevated
							(4.1) in the
							setting of a
							large PDA
Case 3	Normal	Normal	Normal	Normal	Mild PH:	Normal	Elevated (4.3)
Before CMV treatment					RVSP > 31 mmHg + RAP
After CMV treatment	Normal	Normal	Normal	Normal	No PH:	Normal	Normal (3.5)
					RVSp > 25 mmHg + Rap
Case 4	Normal	Normal	Normal	Normal	Pulmonary pressures raise0.5ex12–2/3	Dilated RV	Normal (3.2)
Before CMV treatment					systemic (sEI 1.6)	(RV: LV 1.23)
After CMV treatment	Normal	Normal	Normal	Normal	Pulmonary pressures	Normal	Normal (3.0)
					< raise0.5ex12systemic (sEi 1.2)

LV: left ventricle, RV: right ventricle, PH: pulmonary hypertension, RVSp: right ventricular systolic pressure, RAP: right atrial pressure, PDA: patent ductus arteriosus, PA: pulmonary artery; sEI: systolic eccentricity index (normal < 1.3); PVR: pulmonary vascular resistance.

3 Case 1

A female infant born at 25 weeks GA was transferred to our institution on postnatal day 33 with a diagnosis of culture negative septic shock and acute renal failure (anuric with an elevated creatinine of 2 mg/dl), despite receiving treatment with broad spectrum antibiotics (vancomycin, gentamicin, piperacillin/tazobactam) and antifungal (fluconazole) therapy. She was noted to have combined metabolic and respiratory acidosis [pH6.98, pCO2 73 torr, base deficit –15 mEq/L], hypotension requiring norepinephrine and hydrocortisone, and HRF requiring escalation to the high frequency jet ventilator (HFJV). She continued to deteriorate with progressive hypotension and hypoxemia despite intensive therapies, therefore an alternative etiology of her sepsis was investigated. She was found to have CMV infection with positive urine culture, respiratory culture from endotracheal tube aspirate and CSF by PCR. CMV blood PCR from her newborn screen blood spot was negative. She received a 21-day course of IV ganciclovir (initially 3 mg/kg every 12 hours due to renal impairment and then 6 mg/kg every 12 hours after resolution of renal impairment) for CMV pneumonitis and central nervous system involvement. Within one week of initiating treatment with ganciclovir, her clinical status improved. She was extubated on postnatal day 42 to non-invasive neurally adjusted ventilator assist (NIV NAVA) and then was subsequently able to be weaned to nasal continuous positive airway pressure (CPAP).

During postnatal week 12, she had an acute respiratory deterioration, requiring escalation from nasal CPAP back to NIV NAVA, with progressive hypoxemia and respiratory acidosis. She underwent a 48-hours sepsis rule out and received broad spectrum antibiotics with negative cultures. The biologic nature of the deterioration was initially thought to be secondary to worsening BPD, for which she received three days of furosemide followed by hydrochlorothiazide, fluticasone inhaler, azithromycin, and a prednisolone course. Repeat TnECHO evaluation revealed evidence of mild to moderate chronic PH, for which she was treated with inhaled Epoprostenol 50 ng/kg/min as an adjunct pulmonary vasodilator. Despite transient interval respiratory improvement, repeat TnECHO one week after starting inhaled Epoprostenol showed interval deterioration with moderate PH [estimated RVSP of at least 65 mmHg] and notched PVRi. A trial of 20 ppm of inhaled nitric oxide (iNO) resulted in only marginal improvement in pulmonary hemodynamics. Due to the lack of improvement in her PVD, continued need for high NIV NAVA support and persistent hypercapnemia, repeat blood CMV PCR was obtained and demonstrated an initial viral load of 171,000 IU/ml for which valganciclovir 16 mg/kg twice daily PO was commenced to complete 6 months of therapy. There was interval improvement in the efficacy of oxygenation, and she was weaned to back to nasal CPAP. TnECHO performed one week after commencement of antiviral therapy showed further improvement in the severity of PH. All pulmonary vasodilators (iNO and inhaled Epoprostenol) were weaned off and she was transitioned to chronic treatment with sildenafil 1 mg/kg q 8 hours PO. Repeat TnECHO prior to discharge showed no evidence of PH [estimated RVSP of 28 mmHg + RAp] and normal PVR. She was discharged home on 1 liter per minute (LPM) of nasal cannula (NC) FiO₂ 1.0 in addition to sildenafil.

4 Case 2

A male preterm infant born was born at 25 4/7 weeks GA after pregnancy complicated by intrauterine growth restriction and fetal ultrasonographic finding of echogenic bowel. Urine CMV was sent at birth for evaluation of prenatal findings of echogenic bowel and was negative. On postnatal day 7 there was an acute decompensation characterized by HRF requiring FiO₂ 1.0 and refractory hypotension requiring vasopressin of 1 milliunit/kg/min and norepinephrine of 0.1 mcg/kg/min. TnECHO showed evidence of severe acute PH [large bidirectional PDA, notched PVR, and RVSP > 61 mmHg + RAp]. Pulmonary vasodilator support was provided with combination iNO of 20 ppm and intravenous milrinone of 0.28 mcg/kg/min to good clinical effect with normalization of his TnECHO markers of pulmonary hemodynamics. He was weaned off all pulmonary vasodilator support by day 18, with no echocardiography evidence of PVD.

Despite improvement in his echocardiogram, he developed progressive hypercapnemia despite escalation in HFJV settings. Repeat TnECHO on day 25 showed interval deterioration with moderate-severe PH [bidirectional PDA (systemic level pressure) and notched PVRi] for which milrinone 0.3 mcg/kg/min was reinstituted without significant echo improvement. Due to the lack of clinical respiratory improvement and worsening TnECHO, alternative etiologies were investigated. Blood CMV PCR was obtained on day 43 which revealed a viral load of 91,000 IU/mL. Intravenous ganciclovir 6 mg/kg q 12 hours IV was initiated based on the refractory and progressive nature of the PVD. TnECHO 10 days after initiation of antiviral therapy showed resolution of PH for which his milrinone was weaned off. Blood CMV PCR was repeated 15 days following treatment and was negative; therefore, ganciclovir was discontinued after 15 days of treatment. He was subsequently able to be extubated to NIV NAVA and had no further evidence of PVD on follow-up assessments. He was eventually discharged home on 1 LPM NC with FiO₂ 1.0.

5 Case 3

A male preterm infant was born at 24 1/7 weeks GA. His clinical history was complicated by hemodynamically significant PDA requiring percutaneous closure on day 34. Twenty-four hours after PDA closure, he developed respiratory instability with profound desaturation episodes necessitating initiation of iNO at 20 ppm due to clinical concern of acute PH. TnECHO evaluation 48 hours after starting iNO showed mildly elevated PVRi of 4.3. iNO treatment was weaned slowly over the coming weeks, however his lung disease remained severe, and he remained ventilator dependent at 36 weeks PMA. Routine TnECHO evaluations continued to demonstrate mild elevation in PVR but no evidence of PH or RV dysfunction. Aggressive respiratory treatment was initiated which included azithromycin, chlorothiazide, fluticasone inhaler, and prednisolone course for BPD management. Due to persistent high respiratory requirements, despite optimization of pharmacologic therapies for BPD, plasma CMV PCR was sent and returned positive with 13,700 IU/ml. Concurrent TnECHO evaluation showed mild PH with an RVSP of 31 + RAp. Antiviral therapy with ganciclovir 6 mg/kg every 12 hours IV was provided for 21 days after which he was transitioned to valganciclovir 16 mg/kg BID PO to complete a 6-month course of treatment. After two weeks of IV ganciclovir, there was marked clinical improvement leading to extubation (38 5/7 weeks PMA) and normalization of the PVD markers on TnECHO. He was eventually discharged home on 1.5 liters LPM NC of FiO₂ 1.0.

6 Case 4

A female infant was born at 26 weeks GA in the setting of a pregnancy complicated by prolonged premature rupture of membrane at 23 weeks. The neonatal course was complicated by a hemodynamically significant PDA requiring percutaneous closure and BPD. By 36 weeks PMA she was weaned to nasal CPAP of 6 cmH₂0 and had no echocardiography evidence of PH. Routine follow-up TnECHO at 50 weeks PMA revealed moderate PH with septal flattening (sEI 1.6) and RV dilation which persisted despite iNO treatment. There was interval respiratory deterioration over the next 4 weeks with escalation of nasal CPAP support to 8 cmH₂0 and oxygen requirement to FiO₂ > 0.75 (from baseline of 0.5), despite optimization of anti-inflammatory pulmonary medications which included azithromycin, fluticasone inhaler, prednisolone course, and a 3-day burst of dexamethasone (0.2 mg/kg twice daily PO). Blood CMV PCR was obtained and returned positive with 6,000 IU/ml. She was treated for 14 days with IV ganciclovir 6 mg/kg q 12 hours and then transitioned to valganciclovir 16 mg/kg BID PO to complete a total of one month of treatment. After initiation of anti-CMV treatment, her respiratory status improved allowing her to be weaned back to her baseline FiO₂ of 0.5 and nasal CPAP of 6 cmH₂0 with improvement in her pulmonary pressures (sEI 1.2) and normalization of RV size by the end of 1 month of treatment. Months later she had further complications of her severe BPD which necessitated tracheostomy and transfer to another facility.

7 Discussion

In this novel small case series, we report progressive respiratory deterioration and echocardiography evidence of PVD which coincided with CMV viremia. Importantly, an improvement in pulmonary vascular hemodynamics and respiratory health was noted after treatment for CMV in all four cases. While several case reports suggest congenital CMV as an etiology for respiratory decompensation and PH [8 –10], to our knowledge there is no literature reporting the association of postnatally acquired CMV and PVD. In extremely premature infants, the pathogenic role of pCMV on the cardiopulmonary system remains largely under described with a lack of quantitative epidemiological studies.

pCMV is a multisystem illness which theoretically increases the risk of inflammatory lung disease; however, studies are conflicting and do not provide a cohesive narrative of the long-term outcomes of infants with pCMV [2]. Although both BPD and PVD are inevitable consequences of extreme prematurity for many infants, the natural history of illness was atypical in our cohort due to the refractory nature of the lung disease and temporal relationship of both clinical and echocardiography resolution to initiation of anti-CMV treatment. Several hypotheses may explain the worsening respiratory status in infants with pCMV including subsequent direct lung damage from necrotizing pneumonia and/or a mononuclear inflammatory process [17]. The impact of lung injury on pulmonary vascular development includes medial wall muscularization leading to elevated PVR and PH. Although, direct CMV-induced lung injury leading to PVD is biologically plausible, there was rapid clinical improvement and early normalization of echocardiography features of PVD observed in our cohort upon initiation of antiviral treatment, whereas improvement was not observed with the use of immunomodulator therapies, including steroids, suggesting an alternate pathogenesis. Therefore, we hypothesize that the pathogenesis of CMV-associated PVD may relate to a direct effect of CMV on the immature pulmonary vascular bed leading to vasculitis and maladaptive vascular responsiveness.

Over the past decade, an association between CMV infection and vascular dysfunction has been identified. One mechanism in which CMV may contribute to PVD is through the activation of inflammatory pathways. In animal models of PH, induction of inflammation and immune responses have resulted in pulmonary artery muscularization and arterial remodeling [18]. Clinical isolates of human CMV have been shown to infect endothelial cells, and the presence of human CMV antigens in endothelial cells triggers inflammation and immune response via secretion of chemokines and neutrophil recruitment [19]. Additionally, CMV infection has been shown in a mouse model to cause arteriolar dysfunction due to decreased endothelium-dependent vasodilation and worsening of venular inflammation [20]. Furthermore, small studies in pediatric and adult populations support that CMV infection can potentially lead to vascular injury and endothelial dysfunction. CMV has been largely studied in transplant medicine due to the increased risk of rejection with CMV infections. Following transplant, CMV infection is associated with thickening of the arteriolar walls during rejection [21], and arteriolar dysfunction [22]. It is interesting that in our cases, despite treatment with iNO, there was no improvement in the severity of PVD until after treatment for CMV. In vitro, CMV infection has also been shown to inhibit endothelial nitric oxide synthase and reduced NO production which leads to endothelial dysfunction [23]. Clinically, CMV-seropositive adults have had impaired responses to NO [3]. A study in adult heart transplant recipients showed an association of CMV infection with more severe transplant arteriopathy, which they attributed to endothelial dysfunction by dysregulation of the endothelial nitric oxide synthase pathway [22, 24]. Perhaps, in addition to suppression of endogenous NO production, CMV also suppresses the therapeutic effect of exogenous iNO. The impact of CMV on the NO pathway in human neonates warrants further studies.

PH associated with BPD carries significant risk of mortality, with a recent meta-analysis reporting a mortality rate of 40% during a 2-year follow-up study of PH in preterm infants with BPD [25]. In addition to the increased mortality, infants with BPD and PH are at increased risk of suboptimal growth, feeding difficulties, neurodevelopmental impairment [26], higher rates of tracheostomy, longer duration of hospital stays, and frequent hospital re-admissions [27]. Evaluation for and treatment of a unifying secondary diagnosis, such as pCMV, may reduce polypharmacy, shorten hospitalization and improve morbidity and mortality. These cases suggest that CMV is a potentially modifiable risk factor in preterm infants with PH/PVD. It is also important to recognize that ganciclovir and valganciclovir are not benign interventions; specifically, treatment has the potential to induce bone marrow suppression and/or liver toxicity, which need to be monitored closely while on therapy [28]. None of the patients in our case series developed any adverse consequences of treatment while admitted to the NICU. We speculate that early consideration of CMV-associated PVD and timely intervention may positively modulate adverse neonatal outcomes and potentially mortality.

We acknowledge that this present study is limited by its retrospective nature, lack of a control population, and small number of patients. Additionally, we were able to assess CMV status at birth in only two patients who had their newborn screen blood spot tested, therefore we are unable to be absolutely certain that the disease was postnatally acquired. Additional there were no maternal CMV serologies or breast milk PCRs available to us, however the purpose of this case series was not to learn why or how these infants were infected with CMV, but rather to discuss the relationship of postnatal CMV infection and pulmonary vascular disease. Finally, detection of CMV viremia by PCR was used as a surrogate for the diagnosis of pneumonitis as it was not clinically feasible to perform lung biopsy or bronchoalveolar lavage. Regardless, the refractory nature of the clinical course and temporal response to anti-CMV treatment lends credence to the potential negative impact of CMV on the immature lung and vascular bed. Currently, there are no guidelines or consensus recommendations by any major academic society regarding treatment of pCMV infection in preterm infants. In addition, there are limited pharmacological data regarding optimal dosing or duration of therapy. The variance in duration of treatment in our four cases resulted from physician preference according to the unique circumstances of each individual case. Outside of case reports, there is little data on treatment of pCMV in preterm infants, making it difficult to determine which infants may benefit from treatment and what interventions are needed as these infants age.

In conclusion, we propose consideration of pCMV infection as a cause of atypical respiratory decompensation and PVD in extremely premature infants; specifically, in cases where PVD is not responsive to standard therapies, or the disease severity is out of proportion to the clinical trajectory. Although our case series is small, it suggests that treatment of extremely premature infants with CMV-associated PVD may have a positive impact on cardiorespiratory health and in some situations may be lifesaving. The optimal time of intervention and duration of treatment needs prospective investigation.

Funding

This research received no external funding.

Institutional review board statement

The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Institutional Review Board of the University of Iowa (protocol code 20140743).

Conflict of interest

The authors declare no conflict of interest.

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