Comparative analysis of F-18 FDG PET/CT images between scrub typhus and systemic lupus erythematosus

Abstract

This study evaluated the use of F-18 fluorodeoxyglucose (FDG) PET/CT imaging to differentiate between scrub typhus and systemic lupus erythematosus (SLE) in patients presenting with lymphadenopathy. We carried out a retrospective analysis of 18 scrub typhus patients and seven SLE patients, using various imaging parameters, including lymph node size, spleen and liver lengths, the distance between the two farthest lesions (D_max), and assessments of glucose metabolism. On FDG PET images, we measured the maximum standardized uptake value (SUV_max) of the lymph nodes, spleen, and liver and the mean standardized uptake value (SUV_mean) of the liver and spleen. The D_max values of scrub typhus patients were significantly longer than those of SLE patients, indicating that lymphadenopathy is more generalized in the patients with scrub typhus. The SUV_max values for the lymph node, spleen, and liver were also higher in patients with scrub typhus, while the SUV_mean of the liver and spleen did not differ between the two groups. This study is the first to compare FDG PET/CT images between these two conditions, suggesting the potential of this imaging modality to provide critical diagnostic distinctions.

Figure 1

FDG PET/CT images of a 49 year-old female patient with scrub typhus and a 63 year-old female patient with SLE. The patient with scrub typhus demonstrates extensive involvement of lymph nodes from both cervical to inguinal areas (A), whereas the patient with SLE shows lymph nodes in the right supraclavicular and mediastinal areas (C). FDG uptake levels in the lymph nodes, spleen, and liver are higher in the patient with scrub typhus (B) compared to those in the patient with SLE (D).

Figure 2

A spherical volume of interest (VOI) 3 cm in diameter is placed on the posterior portion of the spleen. The patient with scrub typhus (A) shows higher SUV_max and SUV_mean than the patient with SLE (B). The SUV_mean of the liver is also measured using a VOI 5 cm in diameter. Like the metabolic parameters in the spleen, the liver also shows higher glucose metabolism in the patient with scrub typhus (C) than in the patient with SLE (D).