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).
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 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).
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).
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.
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.
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): 118
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 with HIV infection. Nucl Med Commun (1995 May) 16(5): 327-35
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