F-18 fluorodeoxyglucose and F-18 fluorothymidine positron emission tomography/computed tomography imaging in a case of neurosarcoidosis

Purpose: F-18 fluorothymidine (FLT) PET/CT is considered more specific for malignancy than F-18 fluorodeoxyglucose (FDG) PET/CT. This case report presents F-18 FLT and F-18 FDG scans of a patient with neurosarcoidosis. Materials and Methods: We describe a 34-year-old man who presented with myelopathic symptoms and signs. The patient's evaluation included serological tests for systemic autoimmunity, CSF analysis, magnetic resonance imaging of the spinal cord and brain, abdominal CT, whole-body F-18 FDG and F-18 FLT PET/CT, and high-resolution chest CT. The patient finally underwent transbronchial mediastinal lymph node biopsy for definite diagnosis. Results: The neurologic symptoms were relapsing and remitting. Magnetic resonance imaging demonstrated corresponding abnormal lesions in the spinal cord. Under a tentative diagnosis of multiple sclerosis, the patient was treated with beta-interferon, which showed no beneficial effect. Abdominal CT for evaluation of unexplained abdominal discomfort revealed abdominal lymphadenopathies. F-18 FDG PET/CT showed multiple symmetrical intense accumulations of F-18 FDG on mediastinal and abdominal lymph nodes, whereas only faint to mild F-18 FLT accumulations were observed. Biopsy of mediastinal lymph nodes indicated nontuberculous granulomatous disease. A final diagnosis of neurosarcoidosis was made, and his clinical symptoms and signs were markedly improved by immunosuppressive treatment. Conclusions: Multiple F-18 FDG-avid lymphadenopathies with mild F-18 FLT uptake can be characteristic findings of sarcoidosis. The combination of F-18 FDG and F-18 FLT PET/CT can be helpful in differentiating granulomatous inflammatory diseases such as neurosarcoidosis from malignancy and in localizing the most appropriate biopsy site of active sarcoidosis.