Joint Program in Nuclear Medicine
AIDS Infectious Scintigraphy
Farshid Bozorgi, MD
J. Anthony Parker, MD PhD
February 27, 1996
Presentation
A 43 year old male with history of AIDS presented with increasing shortness
of breath, non-productive cough, and fever for two days. Chest x-ray showed
bilateral interstitial and alveolar infiltrates. Gallium scan was ordered
to rule out pneumocystis carinii pneumonia (PCP).
Imaging Technique
Ten mCi of gallium citrate was injected intravenously, and the whole body
planar images and SPECT views of the chest were obtained.
Spot views of the planar images were acquired for 5 minutes each. A
medium energy collimator was used. Photopeak was centered on 93, 184, and
300 Kev, with 20% window. SPECT view were obtained with continuous acquisition
at 6 degrees (20 seconds each).
Imaging Findings
On Gallium scintigraphy, diffuse bilateral increased
lung uptake suggestive of Pneumocystis Carinii Pneumonia (PCP) were noted
(small arrow). Cardiac silhouette was seen
(large arrow)
Discussion
AIDS patients are susceptible to a variety of bacterial, viral, protozoal,
fungal, and viral infections. Scintigraphy of the more common entities
such as Pneumocystis Carinii Pneumonia (PCP), Toxoplasmosis, Mycobacterium
Avium-Intracellulare (MAI) Infections, and Cytomegalovirus (CMV) Infections
will be discussed.
PCP
PCP is one of the most common pulmonary infections in the adult AIDS patients.
It has traditionally been considered as a protozoa, although it has some
similarities to the fungi (including yeast formation and special staining).
It has a worldwide distribution. Most children are exposed by an early
age. Besides AIDS, other predisposing clinical conditions for PCP include
primary immunodeficiency diseases, immunosuppressive drugs and corticosteroids,
premature malnourished infants, protein malnutrition and etc.
Presentation, course, and response to the treatment in PCP are different
in AIDS and non-AIDS patients. In AIDS patients, the presenting symptoms
are usually more subtle, sputum has a high diagnostic yield for the microorganism,
duration of the therapy is longer, intolerance to antibiotics is high and
the prognosis is poor.
Gallium uptake in PCP is typically diffuse, and occasionally, specially
in the patients on suppressive therapy, focal increased uptake is noted
in the lungs. Gallium scan has a higher sensitivity and specificity in
diagnosis of PCP than CT scan (1) and chest x-ray (2). Quantitative methods
have been used to follow the effects of the treatment. Labeled white blood
cells scans are less useful in PCP because of inflammatory response incited
by the organism.
Toxoplasmosis
Toxoplasmosis is another common infection seen in the AIDS population.
Some articles report that 3-70% of the healthy adults in the United States
have been infected. Four types of infection has been described in toxoplasmosis
including acute, latent, reactivation, and reinfection.
Toxoplasmosis is the most common cause of intracerebral mass lesions
in AIDS patients. Involvement is usually multifocal, however, single lesions
are occasionally found. Contrast-enhanced CT scan shows nodular or ring
enhancement in 90% of the patients, but rarely focal contrast uptake is
not seen. When CT scan is normal or suspicion is high, MRI may be useful.
In AIDS patients, serologic tests rarely confirm the diagnosis, and
a brain biopsy is necessary for definitive diagnosis. There are very few
articles in the literature describing the role of scintigraphy in the differential
diagnosis of lymphoma and toxoplasmosis in AIDS patients with multiple
ring enhancing brain lesions. Most of the articles are based on differential
thallium uptake by these two disease entities. In one of these articles
by Ruiz A, et al (3), none of the 24 patients with toxoplasmosis had thallium
uptake, and all the patients who had intense focal thallium uptake had
lymphoma confirmed by biopsy or autopsy. Increased gallium uptake in the
cerebral toxoplasmosis has been described in the past (4).
MAI
One the bacteria commonly causing infections in the AIDS patients is MAI,
which has been more recently described as Mycobacterium Avium Complex (MAC)
because of several existing strains. In non-AIDS patients lungs are the
most common site of infection, symptoms are usually mild, pre-existing
bronchopulmonary disease is a frequent finding, and treatment success depends
on the underlying cause. In AIDS patients, symptoms are usually of gradual
onset, there is frequently widespread dissemination, and treatment has
been generally unsatisfactory.
Gallium scan has been the most common scintigraphic study performed
in AIDS patients with MAI infection, because usually the sites of infection
have increased gallium uptake. However, some authors (5) have found gallium
insensitive in this regard. The role of In-111 labeled human IgG has been
evaluated recently and showed higher sensitivity and specificity than chest
x-ray (8).
Cytomegalovirus Infections
CMV is another cause of serious infections in the AIDS population. General
rule of herpes viruses applies to CMV ("Once infected, always infected").
Modes of transmission is blood, sexual, or during pregnancy and perinatal.
Clinical manifestations of the CMV infection in AIDS patients include febrile
mononucleosis (most common), interstitial pneumonia, hepatitis, GI syndromes
such as colitis, and pancreatitis, retinitis, meningoencephalitis, encephalopathy,
and endocrinopathy.
Palestro CJ et al studied a case of AIDS patient with fever, in whom
In-111 labeled leukocyte scan showed pancolitis but gallium scan did not
show more than normal excretion of the tracer. Colonic biopsy confirmed
the diagnosis of CMV colitis.
Conclusions:
Scintigraphic studies of the infectious manifestations of AIDS can be a
very helpful tool for the clinicians taking care of these patients, since
they provide non-invasive, convenient ways at a reasonable cost to diagnose
these diseases early in the patient's clinical course, leading to significant
decrease in morbidity or early mortality. Gallium scintigraphy has been
traditionally the first line of scans used in the evaluation of AIDS patients
with fever. However, some authors recommend labeled white blood cells scan
as the first line studies for those febrile patients without localizing
signs, and use gallium scan for those patients whose symptoms are predominantly
pulmonary. If there is a clinical suspicion for PCP infection, or a neoplastic
process as an underlying cause for the fever, gallium is the preferred
radiopharmaceutical. More well controlled studies are needed to compare
the value of these different scintigraphic methods in evaluation of AIDS
with infections.
References
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and computed tomography in the diagnosis of pneumocystis carinii pneumonia
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387-94
2. Moser E., Tatsch K. et al: Value of gallium-67 scintigraphy in primary
diagnosis and follow-up of opportunistic pneumonia in patients with AIDS.
Lung (1990) 168 Suppl: 692-703
3. Ruiz A., Ganz WI, et al: Use of thallium-201 brain SPECT to differentiate
cerebral lymphoma from toxoplasma encephalitis in AIDS patients. AJNR Am
J Neuroradio (1994 Nov) 15(10): 1885-94
4. McLean RG, Murray IP: Gallium scintigraphy in cerebral toxoplasmosis.
Clin Nucl Med (1984 Oct) 9(10): 592-3
5. Garcia R., Pena JM, et al: Comparative study of gallium-67 citrate
scan and Tc-99m human polyclonal immunoglobulin scintigraphy in HIV seropositive
patients with pulmonary infections. Int Conf AIDS (1992 Jul 19-24) 8(3):
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6. Fineman DS, Palestro CJ, et al: Detection of abnormalities in febrile
AIDS patients with In-111 labeled leukocyte and Ga-67 scintigraphy. Radiology
(1989 March) 170(3 Pt 1) :677-80
7. Palestro CJ, Kim CK, et al: In-111 labeled leukocyte and Ga-67 scintigraphy
in cytomegalovirus colitis. Clin Nucl Med (1990 Nov) 15(11) :848
8. Buscombe JR, Oyen WJ, et al: A comparison of In-111-HIG scintigraphy
and chest radiology in the identification of pulmonary infection im patients
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J. Anthony Parker, MD PhD, Tony_Parker@bidmc.harvard.edu