CASE REPORT

An unusual case of thrombocytosis associated withconcurrent cytomegalovirus and respiratorysyncytial virus infection in an immunocompetentinfant: possible roles of thrombopoietin andinterleukin-6

Izumi Akaboshia,*, Kaoru Fugitab, Akio Abeb, Toshio Tanakab

aAkaboshi Paediatric Clinic, 1-16-16, Kuwamizu-machi, Kumamoto, JapanbSpecial Biochemistry and Cellular Immunology Section, SRL, Inc., Tokyo, Japan

Accepted 12 September 2004

01do

KEYWORDSCytomegalovirus;Respiratory syncytial

virus;Thrombocytosis;Thrombopoietin;Interleukin-6

63-4453/$30.00 Q 2005 The Britishi:10.1016/j.jinf.2004.09.014

* Corresponding author.E-mail address: akaboshi@orange.o

Abstract This is the case study of concurrent cytomegalovirus and respiratorysyncytial virus infection in an infant who showed thrombocytosis, liver dysfunctionand bronchiolitis. The combination of thrombocytosis with this co-infection iscausally related to elevated levels of thrombopoietin and interleukin-6. This studyrepresents the first such case ever recorded.Q 2005 The British Infection Society. Published by Elsevier Ltd. All rights reserved.

A congenital or acquired cytomegalovirus (CMV)infection affecting megakaryocytes or plateletsmay induce thrombocytopenia, but not thrombocy-tosis.1,2 An association between respiratory syncy-tial virus (RSV) infection and thrombocytosis hasnot been previously reported. Secondary throm-bocytosis in acute infections is caused by theelevation of circulating thrombopoietin (TPO), inconjunction with interleukin-6 (IL-6).3 To ourknowledge, there have been no reports ofsimultaneous CMV and RSV infections and throm-bocytosis caused by increased serum levels of TPOand IL-6.

Infection Society. Published by

cn.ne.jp (I. Akaboshi).

Described here is the case of an immunocompe-tent infant with thrombocytosis associated withcocurrent CMV and RSV infections, in which totalrecovery occurred spontaneously without specifictherapy.

Case report

A previously healthy 1-month-old Japanese boyexhibited 2 days of a low-grade fever, wheezing,wet cough, and rhinorrhoea. The pregnancy andbirth had been free of complication and he hadbeen breast-fed. On physical examination, a hepa-tomegaly was found, palpable 3.0 cm below thecostal margin in the right mid-clavicular line, as

Journal of Infection (2005) 51, e97–e100

www.elsevierhealth.com/journals/jinf

Elsevier Ltd. All rights reserved.

Figure 1 Changes in platelet counts, IL-6 and serumTPO (A), in serum AST, ALT and CRP (B), in CMV antibodiesindexes to IgM or IgG (C).

I. Akaboshi et al.e98

well as no jaundice, and audible wheezes. He wasdiagnosed with an RSV infection using a nasal swaband a rapid detection of enzyme immunoassay kit(TestPack RSV, Abbot Laboratories).4 A chest radio-graph revealed only mild infiltrates of the rightlower lung. He had a mild lower respiratory tractinfection caused by RSV at 40 days of age, butrecovered spontaneously after 2 days, withouttherapy.

At first evaluation, laboratory examinationsshowed mild liver dysfunction, slight hyperbilirubi-nemia (aspartate aminotransferase 111 IU/l; ala-nine aminotransferase 112 IU/l; lactatedehydrogenase 332 IU/l; total bilirubin 1.7 mg/dl;direct bilirubin 0.9 mg/dl; CRP 1.7 mg/dl), andthrombocytosis (638!109/l) with an absence ofatypical lymphocytes in peripheral blood. Plateletcounts were determined by automated analysis.

A specific IgM antibody to CMV was detectedusing an antibody capture enzyme immunoassay(EIA), and a specific IgG antibody was detected byan indirect EIA (Cytomegalo IgM and IgG antibodydetection kit II; Denka Seiken, Japan).5 The CMVspecific IgM and IgG antibody indexes at 40 days ofage were positive (2.60 and 14.7, respectively),with no evidence of primary infection of HerpesSimplex Virus, Epstein-Barr Virus, Hepatitis B or C.

PCR for detection of CMVDNA was modified fromprevious methods.6 DNA was extracted from 200 mlof the patient’s serum using QIAamp DNA Blood minikit (Qiagen, Hilden, Germany). The PCR primersused in this assay were 5 0-TTA GTG AAC CGT CAGATC GC-3 0 and 5 0-GCA TGC ATA AGA AGC CAA GG-3 0

for major immediate early gene of CMV. When liverenzyme levels were at their highest, at 40 days and2 months of age, the CMVDNA in sera weredetectable by the PCR assay, as shown in Fig. 1.

There had been no clinical symptoms of acongenital CMV infection, such as neurologicalabnormalities or hearing loss. The mild increasedserum levels of aspartate aminotransferase (AST)and alanine aminotransferase (ALT) gradually nor-malized, and hyperbilirubinemia improved rapidly.

Thrombocytosis (more than 450!109/l) per-sisted until 5 months of age (maximum platelets;724!109/l). In spite of thrombocytosis theserum level of TPO at 40 days of age, as determinedby modified sandwich enzyme-linked immuno-sorbant assay (ELISA), was about 4 times higher(10.36 fmol/ml) than that of convalescence(2.26 fmol/ml), and fell slowly.7 The lower limitof detection for TPO was 0.2 fmol/ml. Normalvalues of serum TPO at 1 month of age and 2–11months of age were 3.77G1.45 and 2.10G0.69 fmol/ml, respectively, as previouslydescribed.8

The serum IL-6 levels, measured by a chemilu-minescent enzyme immunoassay, were significantlyhigher at 40 days and 4 months of age (31.8 and38.5 pg/ml, respectively) than at 3, 5 or 6 monthsof age. According to the Fuji Rebio IL-6 kit, thelower limit of detection was 0.2 pg/ml, and thenormal value of IL-6 was !4.0 pg/ml.9

IgM antibodies to CMV decreased gradually, anddropped to 0.54 index value at 6 months of age. Incontrast, IgG antibodies to CMV increased to 68.3index value at same age.

Although the slightly elevated serum level of CRPat 40 days of age was normalized 3 days later, at 4months of age it increased again slightly, withevidence of a transient common cold (Fig. 1). Thepatient remained asymptomatic without anyrelapse of liver dysfunction until 18 months ofage, and showed no mental and motor impairment.

Discussion

Approximately 90% of congenitally CMV infectedinfants are asymptomatic at birth, but these infantsare more likely to experience sequelae, includingsensorineural hearing loss and neurological impair-ment.10 However, the majority of infants with

Unusual case of thrombocytosis in an immunocompetent infant e99

perinatal and postnatal CMV infection remainasymptomatic. Primary and acquired CMV infectionin immunocompetent infants are generally self-limiting and only last for a few months. Infantsgenerally acquire a CMV infection by transmissionfrom the mother in the immediate perinatal or earlypostnatal period.11 A significant proportion ofinfants who have acquired CMV infection exhibitclinical evidence of benign hepatitis, presentedwith symptoms such as jaundice, hepatomegaly,and liver dysfunction.12 It is difficult to diagnoseCMV hepatitis in infants because the definition ofthe disease is less clear, and diagnosis may requirethe presence of a cytomegalic inclusion body, CMVantigens, and genomes, from a hepatic lesionobtained by a liver biopsy. The case presentedhere had appeared to be mild CMV hepatitis in spiteof not performing a liver biopsy. The diagnosis ofacquired CMV infection was based on serologicalinvestigations with the presence of specific IgMantibodies and increasing indexes of IgG antibodies,and CMV viremia with the evidence of directdetection of CMV DNA in sera, as shown in Fig. 1.

Eisenhut M et al. described 27 ventilated childrenwith severe RSV bronchiolitis complicating hepa-titis.13 However, it is believed in our case that liverdysfunction was caused by CMV infection, since ourinfant spontaneously recovered from mild RSVbronchiolitis without mechanical ventilation.

D.A. Tristram et al. reported a 2-month-oldinfant with simultaneous RSV bronchiolitis andCMV infection, associated with hepatitis andthrombocytopenia.14 But, as far as we know, ourpatient is the first case of thrombocytosis with asimultaneous CMV hepatitis and RSV bronchiolitis.

The mechanism of the thrombocytosis found inthe patient seems to be caused by an increase ofserum TPO and IL-6, which might be induced bysimultaneous CMV and RSV infection, or other viralinfection.

Many cytokines and factors, including TPO, IL-6receptor, IL-8, stem cell factor and IL-11, have anability to increase platelet numbers.15 TPO and IL-6are identified as the most important and potentthrombopoietic factors.16,17 Inflammatory throm-bocytosis has been thought to be related toelevated IL-6 levels, which induces the productionof acute-phase proteins such as CRP by hepato-cyte.17 In addition, it has been suggested that IL-6acts through the mediation of TPO to increaseplatelet counts.18 In our case, IL-6 values weresignificantly correlated with CRP, platelet counts,and the TPO level, except for the TPO level at 4months of age.

Of interest, our case showed that serum elevatedTPO did not precede thrombocytosis, although

other research has found this to be true.3 A possibleexplanation for the difference could be the occur-rence of concurrent infection with RSV in additionto the process of CMV hepatitis. However, the exactreason was unclear. Further investigations areneeded to clarify the role of cytokines and otherfactors in CMV hepatitis associated withthrombocytosis.

Acknowledgements

The authors thank SRL for performing the EIA forCMV antibodies.

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