Incidental Global Hypometabolism in the Brain of Patient with AIDS-related Dementia Seen on 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography

Fluorodeoxyglucose positron emission tomography (FDG-PET) has a major role to play in the management of human immunodeficiency virus (HIV)-infected patients. It is able to detect any inflammatory/infectious lesions, which are commonly seen in these patients.[123] HIV-1 related dementia is the most severe form of neurocognitive disorder in patients with AIDS. It is relatively uncommon in postantiretroviral therapy (HAART) era and is associated with a high cerebrospinal fluid/plasma viral load.[4] Functional imaging using PET/computed tomography (CT) has been found to be more sensitive than morphological imaging (magnetic resonance [MR]) in diagnosing this condition before any visible focal lesions/cerebral atrophy.[567] We present the case of a 36-year-old male with AIDS, where global brain hypometabolism was noted incidentally on FDG PET/CT referred for identification of the infective focus/malignancy causing the fever. He was found to be HIV-positive recently and was on HAART for 1 month. He presented with fever with chills for 1 month. On evaluation, recent blood tests showed very high levels of plasma HIV-1 RNA (1162467 copies/ml) and low CD4 cells/CD8 cells ratio (0.07). PET/CT showed hepatomegaly (craniocaudal length 17 cm) and splenomegaly (craniocaudal length 15 cm) with diffusely increased metabolic activity in the liver (SUV max 6.81) and spleen (SUV max 5.39) [Figure 1a and b] due to high viral load.[12] Diffuse ground glass opacification was seen in bilateral lung fields with diffuse low-grade metabolic activity (SUVmax 2.33) [Figure 1a and b] suggestive of infective etiology.[8] Blood culture showed methicillin-resistant Staphylococcus aureus, and he was started on antibiotics. Coincidentally, there was global hypometabolism noted in the cerebral cortex with relatively preserved metabolism in the basal ganglia [Figure 1a and c]. Early precombination antiretroviral (cART) therapy studies using 18F-FDG PET have shown consistently the presence of subcortical hypermetabolism in the basal ganglia, striatum, and thalamus of HIV-positive patients with early stages of HIV-associated dementia, as well as asymptomatic HIV-positive individuals, suggesting that increased glucose metabolism of subcortical structures, such as the basal ganglia, are characteristic of HIV-associated neurocognitive disorders in patients without cART. A limited number of studies have investigated the impact of cART on cerebral glucose metabolism using 18F-FDG PET. There are few publications showing the brain hypometabolism in AIDS-related dementia in patients taking HAART.[910] In our case, axial PET images of the brain [Figure 1a and c] show globally reduced tracer uptake in bilateral cortices. The brain PET images were analyzed using NeuroQTM software, which showed globally reduced cortical metabolism predominantly in bilateral frontal, parietal, and temporal cortex with preserved metabolism in the basal ganglia. On examination, the patient showed severe cognitive and motor decline with stage 3 on Memorial Sloan Kettering AIDS dementia complex scale.[11] Through this case, we wish to demonstrate the additional role of PET/CT in the clinical management of HIV-related dementia. This may be used as an additional tool for diagnosis and probably later for the treatment response assessment in AIDS-related dementia. Brain global hypometabolism has been reported due to other causes of infection leading to metabolic abnormalities such as Human herpesvirus 6 encephalitis.[12] The brain MR imaging findings in patients with sepsis are also studied.[13] It would be worthwhile to observe and evaluate FDG brain PET findings in patients with sepsis and cognitive impairment in further studies.

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Figure 1 (a) Maximum intensity projection image showing diffuse bilateral lung uptake (red arrow), diffuse increased fluorodeoxyglucose uptake in hepatosplenomegaly (blue broad arrows), and globally reduced uptake in the brain (blue arrow) with relatively preserved metabolism in the basal ganglia. (b) Coronal image of positron emission tomography/computed tomography showing diffuse bilateral lung uptake (red arrow), diffuse increased fluorodeoxyglucose uptake in hepatosplenomegaly (blue broad arrows). (c) Axial positron emission tomography images of brain showing globally reduced tracer uptake in brain cortex with preserved uptake in the basal ganglia

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