ORIGINAL COMMUNICATION Diagnostic utility of FDG-PET in neurolymphomatosis: report of five cases Hisanori Kinoshita 1 • Hodaka Yamakado 1 • Toshiyuki Kitano 2 • Akihiro Kitamura 1 • Hirofumi Yamashita 1 • Masakazu Miyamoto 1 • Takefumi Hitomi 3 • Tomohisa Okada 4 • Yuji Nakamoto 4 • Nobukatsu Sawamoto 1 • Akifumi Takaori-Kondo 2 • Ryosuke Takahashi 1 Received: 6 March 2016 / Revised: 31 May 2016 / Accepted: 1 June 2016 Ó Springer-Verlag Berlin Heidelberg 2016 Abstract Neurolymphomatosis (NL) is a rare condition involving the infiltration of lymphoma cells into the peripheral nervous system. NL can be primary or secondary in the setting of an unknown or known hematologic malignancy, respec- tively. Here, we report five cases in which F-18 2-fluoro-2- deoxy-glucose positron emission tomography/computed tomography (F-18 FDG-PET/CT) had great value for diag- nosing NL. Two cases were rare primary NL, and the other three were secondary NL. Clinical presentations were asym- metric sensorimotor disturbances in the extremities with or without involvement of cranial nerves. Furthermore, all patients experienced spontaneous pain in the face or affected extremities. Cerebrospinal fluid analysis was cytologically negative in two of five cases. Gadolinium (Gd)-enhanced magnetic resonance imaging (MRI) detected abnormalities in the cranial nerves, nerve roots, and cauda equina in all cases except case 1 and the recurrent stage of case 2. F-18 FDG- PET/CT showed clear visualization of almost all the lym- phomatous involvement of peripheral nerves and other tissues in all patients. Furthermore, F-18 FDG-PET/CT detected abnormalities including asymptomatic lesions that were not detected with MRI, and also identified the appropriate lesion for diagnostic biopsy. However, as in case 3, the lesions in the left oculomotor nerve and the cauda equina were detected only with Gd-enhanced MRI, which has superior spatial resolution. In conclusion, F-18 FDG-PET/CT is a sensitive modality that can suggest the presence of malignancy and identify appro- priate places for diagnostic biopsies. It is especially useful when combined with Gd-enhanced MRI, even in patients with primary NL that is usually difficult to diagnose. Keywords Neurolymphomatosis Á Lymphoma Á MRI Á FDG-PET Á Painful neuropathy Introduction Neurolymphomatosis (NL) is a rare condition involving the infiltration of lymphoma cells into the peripheral nervous system [1, 2]. NL can be primary or secondary in the set- ting of unknown or known hematologic malignancies, respectively [1]. Diagnosis of NL can be challenging, as the analysis of cerebrospinal fluid (CSF) and magnetic resonance imaging (MRI) is often negative [1]; nerve biopsy is also of limited use because of the frequent proximal and focal involvement of NL [3, 4]. In this study, we identified five patients who were diagnosed with NL between 2010 and 2015. All patients underwent CSF analysis, gadolinium (Gd)-enhanced MRI, and F-18 2-fluoro-2-deoxy-glucose positron emission tomography/computed tomography (F-18 FDG-PET/CT). Two patients were reexamined during the remission and relapse phases. We concluded that F-18 FDG-PET/CT is a highly sensitive and reliable tool for the initial diagnosis and detection of recurrence of NL. & Hisanori Kinoshita hkino@kuhp.kyoto-u.ac.jp & Hodaka Yamakado yamakado@kuhp.kyoto-u.ac.jp 1 Department of Neurology, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan 2 Department of Hematology and Oncology, Kyoto University Graduate School of Medicine, Kyoto, Japan 3 Department of Clinical Laboratory Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan 4 Department of Diagnostic Imaging and Nuclear Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan 123 J Neurol DOI 10.1007/s00415-016-8190-4