AIDS and Nuclear Medicine
Paul J Roach MB BS FRACP
J Anthony Parker MD PhD
February 1st, 1994
A 42 year old homosexual male presented with a 3 week history of fevers and sweats. He denied respiratory symptoms such as cough or sputum. He was diagnosed as HIV positive 5 years earlier but had not manifest with lymphadenopathy or opportunistic infections.
CXR was normal. Gallium-67 scintigraphy revealed diffuse lung uptake. Washings from fibreoptic bronchoscopy confirmed pneumocystis carinii (PCP) infection.
The Boston Globe recently reported (January 26th 1994) that AIDS is now the major cause of death in the 25-44 age group in Massachusetts, especially in blacks and hispanics. As with all other areas of medicine, nuclear medicine is playing an increasing role in the evaluation of AIDS patients, particularly in the diagnosis and follow up of patients with infection and neoplasia.
The most common opportunistic infection is PCP which affects 65%-80%. Other protozoal infections include crytosporidia and toxoplasmosis (abscess, encephalitis). Viral infections include cytomegalovirus (retinitis, adrenalitis, lungs, neurological, disseminated) and herpes viruses (simplex and zoster). Fungal infection include candida (esophagitis), cryptococcus neoformans (meningitis, pneumonitis, disseminated) and Histoplasmosis. Although less common, bacterial infections (especially Streptococcus and haemophilus) are being seen more frequently in children and IV drug users. Other bacterial infections encountered include Listeria monocytogenes, Salmonella, Nocardia and mycobacteria - both tuberculum (TB) and avium intracellulare (MAIS).
Gallium scintigraphy is abnormal in over 90% of cases of PCP and in the presence of grade 3 or 4 uptake and normal CXR is almost 100% specific. Diffuse lung uptake may occur with other processes such as CMV, cryptococcus, bacterial pneumonia and mycoplasma infections as well as vasculitis and lymphoma. Focal lung uptake may occur with bacterial infections, MAIS and rarely with PCP. Gallium-67 uptake in lymph nodes may be seen with mycoplasma, lymphoma and rarely with PCP and toxoplasmosis. Certain appearances on Gallium scintigraphy may improve specificity e.g. retinal, adrenal, renal, colonic and oesophageal uptake suggests CMV, lymph node and lung uptake suggests MAIS (or lymphoma) and extension from lungs into soft tissues is suggestive of fungal infection.
Aerosol transfer of DTPA has also been used in diagnosis and follow up of patients with PCP. While normal patients (including smokers) typically show slow monoexponential clearance of nebulized 99mTc-DTPA from the lungs, patients with PCP (and legionella), due to type 1 pneumocyte destruction, show rapid biphasic washout curves. This rapid and simple test has been found to be over 85% sensitive and specific in PCP diagnosis in AIDS patients and has been shown to be more useful than Gallium-67 scintigraphy in diagnosis of PCP.
In the evaluation of fever of unknown origin (FUO), 111In WBC have been shown to be more sensitive than gallium-67 however, neutropenia (related to disease and treatment such as AZT and gancyclovir) as well as risks associated with venepuncture and labelling procedures may complicate use of this technique. Small studies using donor WBC and polyclonal Immunoglobulin have shown promising results.
Disorders include encephalitis (dementia), infection (especially cryptococcus, toxoplasmosis and CMV) and malignancy (primary cerebral lymphoma). SPECT typically shows multiple focal perfusion defects (a pattern identical to cocaine abuse) and may be abnormal before atrophy appears on CT or MRI imaging. PET studies using 18F-FDG have shown subcortical hypermetabolism followed by cortical and subcortical hypometabolism in the later stages. Improvement in cerebral metabolism has been demonstrated following therapy with AZT. Reduced perfusion of the basal ganglia and increased background activity have also been reported on brain SPECT studies using 99mTc HMPAO. Tumours typically show increased uptake of 18F-FDG as well as 201Tl.
The commonest tumour is Kaposi's sarcoma (arising from vascular + ?lymphatic endothelium). It is rarely seen in children and IV drug users. Typically negative on Gallium-67 scintigraphy, the tumour usually will concentrate 201Tl. Gallium-67 is useful in the diagnosis and follow up of patients with lymphoma, including Non-Hodgkins lymphoma, the commonest lymphoma in patients with AIDS.
DISIDA scanning has been reported to be 90% sensitive in the detection of AIDS sclerosing cholangitis. Bone scans may be useful in patients with lymphoma, bacillary angiomatosis (a rickettsial infection causing Kaposi sarcoma-like skin lesions and distant abnormalities on 35% bone scans) and in myositis (caused by AZT and KS).
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J. Anthony Parker, MD PhD, firstname.lastname@example.org