LUNG.html
ORIGINAL ARTICLE
Lung fibrosis in deceased HIV-infected
patients with Pneumocystis pneumonia
E J Shaddock, MB BCh,
FCP (SA)
G A Richards, MB BCh,
FCP (SA), PhD
Division of Pulmonology and Critical Care,
Department of Medicine, Charlotte Maxeke Johannesburg Academic Hospital
and University of the Witwatersrand, Johannesburg
J Murray, MB BCh, FFPath (SA)
National Institute of Occupational Health of the
National Health Laboratory Services and School of Public Health,
University of the Witwatersrand
Corresponding author: E Shaddock (eshaddock@metroweb.co.za)
Background.
Pneumocystis pneumonia (PcP) is one of the most common opportunistic
infections found in patients with HIV. The prognosis if ventilation is
required is poor, with mortality of 36 - 80%. Although more recent
studies have shown improved survival, our experience has been that
close to 100% of such patients die, and we therefore decided to
investigate further.
Methods.
All patients with confirmed or suspected PcP who died owing to
respiratory failure were eligible for the study. Where consent was
obtained, trucut lung biopsies were performed post mortem, stored in
formalin and sent for histopathological assessment.
Results.
Twelve adequate lung biopsies were obtained from 1 July 2008 to 28
February 2011 – 3 from men and 9 from women. The mean age was 34.7
years (range 24 - 46), and the mean admission CD4 count was 20.8 (range
1 - 68) cells/μl and median 18.5 cells/μl. All specimens demonstrated
typical PcP histopathology; in addition, 9 showed significant
interstitial fibrosis. Three had co-infection with cytomegalovirus
(CMV), two of which had fibrosis present. There was no evidence of TB
or other fungal infections.
Conclusion.
The high mortality seen in this cohort of PcP patients was due to
intractable respiratory failure from interstitial lung fibrosis.
Whereas the differential includes ventilator induced lung injury, drug
resistance or co-infections, we suggest that this is part of the
disease progression in certain individuals. Further studies are
required to identify interventions that could modify this process and
improve outcomes in patients with PcP who require mechanical
ventilation.
S Afr J HIV Med 2012;13(2):64-67.
Since the
introduction of antiretroviral therapy (ART) for individuals who are
HIV-infected with AIDS, there has been a dramatic decline in the number
of these patients presenting with Pneumocystis jerovicii pneumonia
(PcP) in the developed world. In South Africa, the antiretroviral (ARV)
rollout was delayed for political reasons until 2004; consequently,
significant numbers of patients are still presenting with PcP as a
cause of respiratory failure. These patients are either unaware of
their diagnosis or have not started ARVs for reasons that include poor
access to medical facilities and drugs, denial and lack of education.
If patients with PcP require mechanical ventilation, the prognosis is
poor, with mortality ranging from 36 - 80%.1
,
2
In fact, prior to the availability of ARVs, such patients were not
mechanically ventilated in South Africa as no definitive therapy was
available. Once these agents became available to all HIV-positive
patients with CD4 counts <200 cells/μl, it became feasible for
them to be considered for ventilation. At the Charlotte Maxeke
Johannesburg Academic Hospital, it soon became apparent that few of
these patients survived, despite early initiation of both ART and
effective chemotherapy for PcP. Management included use of ARDSNET low
tidal volume strategies,3
conservative fluid protocols, adjunctive corticosteroids and minimal
sedation. Despite these, mortality remained extremely high while other
units were reporting 50 - 79% cure rates.1
,
4
It was consequently decided to prospectively investigate the patients
who had died in the unit, with the aim of determining the causes of
failure of therapy. Possibilities that had been considered for this
failure were concurrent infections including cytomegalovirus,5
,
6
Cryptococcus neoformans, mycobacterial or bacterial infections such as Streptococcus pneumonia, drug resistance, as well as pulmonary Kaposi’s sarcoma.7
Methods
This was a prospective study to investigate
histological findings of patients who died from confirmed or suspected
PcP. All patients in these two categories, with respiratory failure,
were considered for the study. PcP was suspected in patients with
clinically advanced HIV presenting with hypoxic respiratory failure
with typical chest radiograph changes, including bilateral diffuse
alveolar infiltrates, granular opacities or, occasionally, unilateral
or focal infiltrates.7
Pneumocystis was confirmed ante mortem
on sputum from 4 of the patients using the Giemsa stain; and 9 had
organisms seen on histological samples. The remaining 3 had markedly
elevated beta-D-glucan (BDG) levels >500 pg/ml.8
Pre-mortem biopsies or bronchial washings were not possible owing to
the severity of the hypoxia. With family consent, multiple trucut
biopsies were taken from different regions of the lungs of each patient
after death. The specimens were stored in formalin and subsequently
stained with Grocott, Gordon and Sweets, Alcian blue, Ziehl-Neelsen and
haematoxylin and eosin. Ethics approval was given by the University of
the Witwatersrand Ethics Committee.
Results
Sixteen lung biopsies were obtained from 1
July 2008 to 28 February 2011. Table 1 lists patient demographics and
laboratory characteristics. Four were inadequate samples and therefore
not included. The final 12 were from 3 male and 9 female patients. Mean
age of patients was 34.7 years (range 24 - 46 years). Mean admission
CD4 count 20.8 (range 1 - 68) cells/μl, and the median CD4 was 18.5
cells/μl.
ICU details
All 12 patients were admitted to the
intensive care unit (ICU), where 10 were mechanically ventilated; none
developed pneumothoraces. All received appropriate high-dose
trimethoprim-sulfamethoxazole (TMP-SMX) with high-dose corticosteroids
as primary management. None were on ART at the time of presentation.
Histopathology
All 12 of the final specimens demonstrated the
typical histopathological pattern of PcP, including alveoli filled with
frothy material, type 2 cell hyperplasia and pneumocystis organisms. In
addition, 9 of the 12 showed evidence of interstitial fibrosis with
expansion of the interstitium by fibroblasts and collagen of varying
degrees of severity. There was significant destruction and distortion
of the lung architecture, resulting in a marked decrease in available
alveolar-endothelial surface area for diffusion (Fig. 1). Three had
evidence of CMV co-infection with intracellular inclusion bodies, and 2
of these also showed evidence of fibrosis. One of the latter 2 had a
super-added bacterial infection that was not evident in any of the
other specimens. There was no evidence of TB or other fungal infection
in any of the specimens.
Discussion
Pneumocystis pneumonia is still one of the most common opportunistic infections found in patients infected with HIV.9
Pneumocystis
is primarily an alveolar pathogen that does not invade the pneumocyte
to which it tightly adheres. The histopathological changes that are
seen are explained by the exuberant host inflammatory response to the
organism, which promotes pulmonary injury in only some patients during
infection. Severe pneumocystis
pneumonia can result in a significant neutrophilic response that leads
to diffuse alveolar damage, impaired gas exchange and respiratory
failure.10
P. jirovecii
has specific proteases that have the ability to damage the lung
interstitium, and endogenous host proteases including matrix
metalloproteinases (MMP) are also secreted in response to an influx of
pro-inflammatory mediators (Interleukin-6 (IL-6), Interleukin-8 (IL-8),
monocyte chemotactic protein-1 (MCP-1), and tumour necrosis factor
alpha (TNF-α)) from alveolar epithelial cells.
11
,
12
This can explain the extensive capillary leak and frothy hyaline
material that fills the alveolus in typical PcP. It is possible that
the extensive effacement of normal alveolar architecture with fibrosis
demonstrated in these biopsies is part of a reparative process that may
occur only in those individuals genetically predisposed to the
development of fibrosis, so that not all patients with PcP behave
similarly.
In our sample, 75% of the patients who died of refractory
respiratory failure revealed varying degrees of interstitial fibrosis
resulting in obliteration of the alveolar capillary interface and loss
of surface area for diffusion with the remainder, demonstrating
unresponsive PcP. The pattern of the former is similar to that of the
fibrotic stage of acute respiratory distress syndrome (ARDS); and,
whereas it might be argued that this could be consistent with ARDS
following an infection by a more virulent organism such as Streptococcus pneumoniae, this organism was not cultured in vivo,
and patients all received standard empiric therapy for
community-acquired pneumonia. Importantly, none presented with the
secondary organ dysfunction or systemic inflammatory response syndrome
(SIRS), more typical of severe infections with this organism. In
addition, all the patients received corticosteroids as a component of
therapy for PcP that may be effective in the therapy of refractory ARDS
owing to other causes.13
Another factor that could be responsible for the fibrotic injury is
ventilator-induced lung injury (VILI). However, 2 of the 13 patients
were not ventilated, and their biopsies showed similar interstitial
fibrotic changes to those who were, and the other 11 were ventilated
with tidal volumes ≤6ml/kg, and were recruited and maintained on
appropriate PEEP, making this explanation unlikely.
In South Africa, where medical resources are limited, the majority
of patients with PcP and respiratory failure (most of whom have PaO2/FiO2 ratios
<200) are treated with oxygen via a re-breathing mask and
appropriate pharmacological therapy in the general wards. Only the most
severely hypoxic patients or those who fail therapy are considered for
ventilation. This observation highlights a weakness in our sample, with
a selection bias for those with a worse prognosis. Patients who were
not considered candidates for ICU admission might have developed
respiratory failure and died in the general medical wards, or more
usually might have made a full recovery despite initial low P/F ratios.
The latter, who in more resource-rich environments would have been
admitted to ICU, could account for the high survival rates in other
studies. Those admitted to ICU in South Africa are preselected, with
most having already received and failed appropriate pharmacotherapy. It
has previously been reported in the pre-ART era that patients who
required ventilation despite adequate and appropriate therapy, have a
poor prognosis.4
The reasons for the failure of therapy and the failure to benefit
from mechanical ventilation have not previously been well described.
Why some patients and not others develop fibrosis has also not been
adequately elucidated. It could be argued that these patients might
have had 2 disease processes: PcP superimposed on a more chronic
condition or that this was an acute exacerbation of a more chronic
underlying inflammatory process similar to those that occur in the
idiopathic interstitial pneumonias.14
However, this does not explain why these patients had elevated β-D
glucan levels in the absence of fungal infection elsewhere, and X-ray
features not compatible with the interstitial pneumonias; and in the
latter case, why the histological features were typical of PcP. CMV has
been postulated to be more than a ‘fellow traveller’ in
patients with PcP, and treatment with gancyclovir has been reported to
improve outcome.5
,
6 It is
conceivable that infection by both organisms could be synergistic
regarding the fibro-proliferative effects. However, in only 3 of our
cohort was there evidence of CMV co-infection, 2 of whom did have
fibrosis.
An important consideration for treatment failure is the possibility of resistance to sulfa drugs owing to mutations of Pneumocystis
dihydropteroate synthase (DHPS) gene due to increased drug pressure
from the widespread use of TMP-SMX prophylaxis. DHPS, the enzyme
responsible for folate synthesis and the target of TMP-SMX, has
undergone gene mutations that have been identified in 56% of P. jirovecii strains in South Africa.15 However, as human strains of PcP cannot be cultured in vitro,
it is difficult to prove that these mutations confer drug resistance. A
number of studies have evaluated the effect of these mutations on
clinical outcomes with conflicting results. Helweg-Larsen et al. demonstrated that patients infected by organisms with a DHPS mutation had a threefold increased risk of death.16 Navin and colleagues, however, found no association with mortality at 6 weeks nor with treatment failure.17 In fact, they found that 85% of patients with DHPS mutations treated with TMP-SMX responded to treatment.
A limitation of our study is the small sample size. In view of our
resource-limited setting, these patients are not often viewed as good
ICU candidates. Therefore, even though the PCP burden in South African
hospitals is high, the available ICU PcP population is restricted. We
feel that these are important data and will add to the understanding of
the clinical course of these patients, even taking into account the
small sample size.
Interstitial fibrosis has previously been demonstrated in
patients who have survived an episode of PcP, as well as on previous
necropsy studies.4
,
18
There have also been histological reports of cryptogenic organising
pneumonia, granulomatous inflammation and diffuse alveolar damage.19
Our cohort, however, was unusual in that the majority of patients with
PcP, most of whom were ventilated, had evidence of extensive pulmonary
fibrosis – which was associated with an extremely poor prognosis.
This phenomenon has been described previously; however, it has not been
highlighted as the probable underlying cause for treatment failure and
death. We suggest that, if we want to improve the dismal outcome of
these patients, we need to consider the state of the underlying lung,
and realise that treatment of the organism alone is insufficient.
Primarily, we need to expand the rollout of ARVs and, failing this, try
to both recognise and treat the condition sooner, prior to the
development of fibrosis. Ideally, we should also develop a management
protocol that addresses the lung fibrosis once it has occurred.
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Table 1. Patient demographics and laboratory characteristics
Patient
Sex
Age (years)
CD4
cells/μl
PcP on sputum
BDG
pg/ml
PcP on histo
CMV on histo
Fibrosis
SM
♂
27
11
N/A
N/A
Yes
No
Present
NM
♀
46
19
Yes
N/A
Yes
Yes
None
MS
♂
40
31
Yes
402
Yes
No
Present
DM
♀
33
1
Yes
>500
Yes
Yes
Present
NS*
♀
44
29
Yes
>500
No
No
Present
XD*
♀
24
n.a.
N/A
>500
Yes
No
Present
NM
♀
28
68
N/A
>500
Yes
No
None
TR
♀
24
22
N/A
>500
Yes
No
Present
NM
♀
25
7
N/A
>500
No
No
Present
AM
♀
46
18
N/A
n.a.
Yes
No
None
TM
♀
41
n.a.
N/A
>500
No
No
Present
JN
♂
38
2
N/A
51
Yes
Yes
Present
*Not ventilated.
N/A=not available.
Fig. 1. Low magnification of alveoli showing normal
interstitium of (a) alveolar walls and (b) alveolar spaces (Gordon and
Sweet stain).
Fig. 2. High magnification showing an enlarged pneumocyte with (a) an intranuclear CMV inclusion (haemotoxylin and eosin stain).
Fig. 3. Low magnification showing (a) frothy exudate filling the alveolar spaces (haemotoxylin and eosin stain).
Fig. 4. Low magnification showing (a) marked expansion of the interstitium by fibrous tissue (Gordon and Sweet stain).
Fig. 5. Higher magnification showing pneumocystis organisms within frothy intra-alveolar exudates (Grocott stain).