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Journal of Clinical Microbiology, February 2002, p. 1496-1499, Vol. 40, No. 4
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.4.1496-1499.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Aspergillus Galactomannan Antigen in the Cerebrospinal Fluid of Bone Marrow Transplant Recipients with Probable Cerebral Aspergillosis
Claudio Viscoli,1,2* Marco Machetti,1 Paola Gazzola,1,3 Andrea De Maria,4 Dimitri Paola,5 Maria Teresa Van Lint,6 Francesca Gualandi,6 Mauro Truini,7 and Andrea Bacigalupo6
Istituto Nazionale per la Ricerca sul Cancro,1
Dipartimento di Oncologia, Biologia e Genetica,2
Dipartimento di Scienze Neurologiche e della Visione,3
Dipartimento di Medicina Interna,4
Dipartimento di Medicina Sperimentale ,5
Dipartimento Diagnostico di Laboratorio, di Anatomia Patologica e Medico Legale, Università di Genova,7
Ospedale San Martino, Genoa, Italy6
Received 10 May 2001/
Returned for modification 26 September 2001/
Accepted 23 November 2001

ABSTRACT
The
Aspergillus galactomannan test was performed on cerebrospinal
fluid and serum samples from 5 patients with probable cerebral
aspergillosis and from 16 control patients. Cerebrospinal fluid
galactomannan levels were significantly higher in aspergillosis
patients, and most galactomannan was produced intrathecally.
Comparison of serum galactomannan values in pulmonary and cerebral
aspergillosis patients showed significant overlapping. Detection
of
Aspergillus galactomannan in cerebrospinal fluid may be diagnostic
of cerebral aspergillosis.

TEXT
Bone marrow transplant recipients are at high risk of developing
Aspergillus infection, due to the combined effects of profound
and prolonged neutropenia and the use of high-dose steroid therapy
for management of graft-versus-host disease.
Although pulmonary infection is the most frequent manifestation of aspergillosis, cerebral disease is not uncommon, being detected in 10 to 20% of all cases of invasive aspergillosis. Most patients die within a few days after diagnosis, with a mortality rate as high as 95% (10). Cerebral involvement can occur even without any pulmonary disease (2). In recent years, a sandwich enzyme-linked immunosorbent assay (ELISA), "Platelia Aspergillus" (Bio-Rad Laboratories, Marnes La Coquette, France), for diagnosis of Aspergillus infection by the detection of galactomannan (GM) antigens, has aroused interest (7, 9, 12, 13). The sensitivity and specificity of this test are good, and it sometimes gives positive results before the onset of symptoms or radiological abnormalities (9, 11, 13, 17). There is some evidence that the test is reliable even when used on bronchoalveolar lavage or cerebrospinal fluids (CSF) (8, 16, 18). In this study we have investigated the value of the Platelia Aspergillus ELISA with CSF specimens for the diagnosis of cerebral aspergillosis. All serum and CSF samples were processed according to the manufacturer's instructions, and ELISA results were tabulated as the ratio of the optical density of the sample tested to the optical density of the threshold positive control (GM index). All comparisons were performed using the Mann-Whitney U test for unpaired data sets. Data were expressed as box plots indicating median values with interquartile ranges to graphically represent the GM index in patient and control groups (StatView 4.2 program; Abacus Concepts, Berkeley, Calif.).
From 1995 to 2000, at the Bone Marrow Transplant Unit of the Hematology Department of San Martino General Hospital in Genoa, Italy, five patients with probable aspergillosis, as defined by the EORTC-MSG (European Organization for Research and Treatment of Cancer-Mycoses Study Group) consensus group (1), were observed. For all patients, albumin, immunoglobulin G (IgG), and glucose concentrations were calculated in parallel, in CSF and serum samples. In addition, the IgG index [calculated as (CSF IgG level/serum IgG level)/(CSF albumin level/serum albumin level)] was also determined as an estimate of intrathecal IgG production (15). The main clinical characteristics are shown in Table 1. In computed tomographic scans all patients had hypodense lesions, with ring enhancement. In no case was a cerebral biopsy performed, because of the patients' underlying conditions and severe thrombocytopenia. All patients died after a median of 40 days after diagnosis. Autopsies were performed for three of five patients and showed diffuse cerebral infiltration with hyaline septate, acute branching hyphae, diagnostic of cerebral mold infection. For these patients, premortem CSF cultures were negative and postmortem cultures were not performed. The two patients who did not undergo autopsy had at least one nasal swab positive for Aspergillus spp. within the 30 days preceding the onset of neurological symptoms. The median CSF GM index for the five patients with probable cerebral aspergillosis (eight samples) was 10.52 (mean, 81.931; standard deviation [SD], 200.958; range, 0.549 to 578.5). By contrast, the median CSF GM index from the 16 control patients (33 samples) was 0.287 (mean, 0.281; SD, 0.13; range, 0.09 to 0.749). As shown in Fig. 1, there was no overlap between the two groups of patients.
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TABLE 1. Clinical characteristics of five bone marrow transplantation patients with probable cerebral aspergillosis
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To rule out the possibility that the presence of GM in CSF was
merely due to passive transfer, the percentage of intrathecally
produced GM was calculated for each patient. The chemicophysical
characteristics of the GM molecule have not been completely
characterized yet. According to the information available (
6),
the fraction of GM reacting with the EB-A2 monoclonal antibody
used in this test is part of a more complex molecule whose molecular
weight is intermediate between those of albumin and IgG. Therefore,
we postulated that the CSF albumin/serum albumin quotient (QAlb),
which indicates the amount of albumin crossing the blood-brain
barrier, could represent a maximal estimate of the amount of
GM crossing the barrier. As shown by the increased QAlb values
(Table
2), all patients had some degree of blood-brain barrier
damage. Based on the QAlb, we calculated the expected CSF GM
index, i.e., the index we should have found if the presence
of GM in CSF were due only to passive transfer. Finally, the
actual CSF GM index was estimated and, for each patient, the
difference between the measured and expected CSF GM indexes
(which indicates intrathecally produced GM) was calculated and
divided by the measured GM index. The final quotient represented
the percentage of intrathecally produced GM. Overall, the median
expected CSF GM index was 0.053 (SD, 0.196), while the median
measured CSF GM index was 26.144 (SD, 252.900). The difference
was highly statistically significant (
P < 0.001). The percentage
of the total CSF galactomannan that was intrathecally produced
ranged from 95.6 to 99.9%.
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TABLE 2. CSF and serum parameters, expected and measured CSF GM index, and percentage of total GM content that was intrathecally produced
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To determine whether patients with cerebral or pulmonary aspergillosis
might be distinguished just on the basis of the serum GM index
(which might render the CSF test unnecessary), the test was
also performed on a second control group of five patients with
documented pulmonary aspergillosis and without cerebral aspergillosis
(45 samples), and these results were compared with those obtained
for our original group of patients with cerebral aspergillosis
(five patients, 56 samples). As shown in Fig.
2, the median
serum GM index was higher in patients with cerebral aspergillosis
(median, 3.05; mean, 6.007; SD, 5.91; range, 1 to 25.709) than
in patients with pulmonary aspergillosis (median, 2.118; mean,
37.154; SD, 212.082; range, 0 to 1,424.14) (
P < 0.01). However,
a box plot analysis showed considerable overlap between the
two groups (95% confidence interval, 4.46 to 7.55 for cerebral
aspergillosis versus -18.39 to 92.7 for pulmonary aspergillosis).
In fact, 78% of the GM index values in patients with cerebral
aspergillosis were contained within the 25th and 75th percentiles
of those obtained from patients with pulmonary aspergillosis.
We recognize that none of our patients with cerebral disease
might be defined as having documented aspergillosis, since in
no case was confirmation obtained by culture from infected tissues.
Three of these patients had autopsy-documented mold infections,
and two had compatible clinical disease with evidence of nasal
colonization. However, all of them had several positive results
by serum GM antigen detection, a test which has been shown to
be sensitive and specific for the diagnosis of aspergillosis.
According to some authorities, positive
Aspergillus GM antigenemia
combined with appropriate clinical signs in patients at high
risk for aspergillosis constitutes evidence which is almost
equivalent to histological documentation of hyphae, even in
the absence of confirmation by culture (
3). In addition,
Aspergillus accounts for most of the cases of brain abscess in bone marrow
transplant recipients (
2), and cross-reactivity for the EB-A2
monoclonal antibody has been demonstrated only with filamentous
fungi, which usually are not involved in invasive infections
(
5,
9,
14). A possible exception is
Fusarium, which, however,
rarely causes isolated cerebral lesions. Moreover, a recent
and specific report seems to exclude any cross-reaction (
14).
For all these reasons, we considered another etiology extremely
unlikely. Other studies have already suggested the potential
value of the GM antigen detection test for diagnosis of cerebral
aspergillosis. Verweij et al. (
16) studied 26 CSF samples from
a single patient with documented
Aspergillus meningitis and
found that the test result became positive 45 days before the
positive CSF culture. Comparison with control CSF specimens
from patients without aspergillosis showed good specificity.
These authors also suggested that the cutoff for CSF positivity
might be lower than the cutoff for serum positivity. Kami et
al. (
4) studied 5 patients with documented cerebral aspergillosis
and 11 controls. They found that the test was 100% sensitive
and specific for the diagnosis of cerebral aspergillosis.
In conclusion, in the present study we showed a statistically significant difference in the CSF GM indexes between patients with cerebral aspergillosis and a control group of patients with other neurological diseases. The great majority of the GM in CSF (95.68 to 99.92%) was apparently produced intrathecally, as shown by the difference between expected and measured CSF GM indexes in cerebral aspergillosis patients. Finally, serum GM indexes seem to be unable to discriminate between patients with pulmonary and cerebral disease, as shown by the remarkable overlapping of values between the two groups. Our study suggests that the Aspergillus CSF GM index might be diagnostic for cerebral aspergillosis in patients at high risk for aspergillosis and with a compatible neurological disease. Further studies on larger patient populations might be necessary in order to fully evaluate the role of this test in the diagnosis of this dreadful disease.

ACKNOWLEDGMENTS
This work was supported by the Ministero della Sanità,
Istituti di Ricerca a Carattere Scientifico (Progetto 120.5/RF98.88),
and the Università di Genova, Genoa, Italy.

FOOTNOTES
* Corresponding author. Mailing address: Istituto Nazionale per la Ricerca sul Cancro, Largo Rosanna Benzi 10, 16132 Genoa, Italy. Phone: 39-010-5600846 or -5600848. Fax: 39-010-5600264. E-mail:
viscolic{at}unige.it.


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Journal of Clinical Microbiology, February 2002, p. 1496-1499, Vol. 40, No. 4
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.4.1496-1499.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.