Case Author(s): Gregg Schubach, M.D. and Keith Fischer, M.D. , 4/5/96 . Rating: #D3, #Q5

Diagnosis: Mycobacterial Infection, unspecified

Brief history:

36-year old HIV-positive man presents with persistent fevers.

Images:

Anterior and posterior gallium images 72 hours after injection

View main image(ga) in a separate image viewer

View second image(ct). Axial CT image near level of SMA origin

Full history/Diagnosis is available below

Diagnosis: Mycobacterial Infection, unspecified

Full history:

36-year old HIV-positive man presents with persistent fevers and palpable supraclavicular adenopathy.

Radiopharmaceutical:

Ga-67 citrate

Findings:

Whole-body planar images in anterior and posterior projections were obtained 72 hours after the administration of Ga-67 citrate intravenously. There is markedly increased activity in the following lymph node regions: right supraclavicular, right mediastinal/paratracheal, right hilar, abdominal, and left iliac. There is also markedly increased radiopharmaceutical uptake in the spleen. The CT study of the abdomen demonstrates extensive, bulky lymphadenopathy in the retroperitoneum.

Discussion:

Gallium-67, which has a physical half-life of 78 hours, is often useful to localize inflammatory lesions and some tumors. Gallium-67 decays by electron capture and has photon energies of 92, 184, 296, and 388 KeV. Gallium-67 citrate binds to transferrin, the plasma protein responsible for iron transport. Gallium-67 binds to lactoferrin in tissues. Lactoferrin is found in high concentrations in salivary glands, lacrimal glands, the nasopharynx, the spleen, and bone marrow. Neutrophils have a high concentration of lactoferrin, which partially accounts for gallium-67 citrate accumulation in abscesses. The liver metabolizes both transferrin and lactoferrin; hence, hepatic uptake of gallium-67 citrate is normal.

15% to 25% of the administered dose is excreted by the kidneys during the first 24 hours. Renal activity on images obtained after 48 hours is abnormal. After 24 hours, the colon is the main route of gallium elimination. The colon, which is the critical organ, receives 0.6-0.9 rads/mCi.

Tumors with transferrin receptors on their surfaces will be gallium-avid. The gallium-transferrin complex is deposited intracellularly.

Gallium scintigraphy plays an important role in the clinical management of patients with AIDS who have fever or respiratory symptoms. This is particularly important in light of the high prevalence of Pneumocystis carinii pneumonia (PCP) in AIDS patients and the high sensitivity (90-96%) of gallium- 67 studies for PCP. While diffuse interstitial infiltrates on chest radiographs may be seen in early cases of PCP, mild prolonged symptoms and normal chest radiographs are common. Kramer, et al., found that 27 of 57 abnormal gallium lung scintigrams were associated with normal chest radiographs. Thus, chest radiographs have a relatively low sensitivity for detecting early lung disease in AIDS patients.

Negative gallium scintigraphy with a positive chest radiograph, however, is often associated with pulmonary Kaposišs sarcoma.

Gallium scintigraphic findings of PCP are diffuse pulmonary uptake distributed either heterogeneously or homogeneously. The sensitivity and specificity of gallium-67 scintigraphy for PCP are 90% and 75%, respectively. While the positive predictive value of abnormally increased pulmonary uptake is only about 60%, the negative predictive value for PCP in a patient with normal gallium scintigraphy is greater than 90%. Therefore, normal gallium scintigraphy makes the diagnosis of PCP very unlikely.

Gallium-67 citrate is also accumulated in other opportunistic infections in AIDS patients, including: disseminated mycobacterium avium-intracellulare (MAI), Candida esophagitis, toxoplasmosis, cytomegalovirus (CMV), cryptococcus, and herpes simplex infections. Gallium-67 also accumulates in lymphoma and uncomplicated bacterial pneumonias, which are both very common in patients with AIDS.

References: 1) Sandler, et al. Diagnostic Nuclear Medicine, 1996. Williams and Wilkins 2) Datz, et al. Nuclear Medicine: a teaching file, 1992. Mosby Yearbook

Followup:

A biopsy of the right supraclavicular lymph node demonstrated an atypical mycobacterial infection.

Major teaching point(s):

While PCP, lymphoma, and bacterial and non-bacterial infections are gallium- avid, Kaposišs sarcoma is not.

Differential Diagnosis List

The differential diagnosis for the adenopathy seen in the chest and abdomen in this patient with AIDS includes lymphoma, tuberculosis, and other mycobacterial infections (e.g., MAI).

ACR Codes and Keywords:

References and General Discussion of Gallium Scintigraphy (Anatomic field:Vascular and Lymphatic Systems, Category:Neoplasm, Neoplastic-like condition)

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Case number: ga005

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