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F-18 Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Muscle Uptake in Antiglutamic Acid Decarboxylase Antibody-positive Stiff-person Syndrome
Address for correspondence: Dr. Koramadai Karuppusamy Kamaleshwaran, Department of Nuclear Medicine, Kovai Medical Center and Hospital Limited, Coimbatore, Tamil Nadu, India. E-mail: dr.kamaleshwar@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Wolters Kluwer - Medknow and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Antiglutamic acid decarboxylase-65 (anti-GAD65) autoantibodies have been identified in variety of rare neurologic disorders most frequently in stiff-person syndrome (SPS), condition characterized by muscle rigidity and overlying painful spasms, typically affecting axial and limb musculature. In anti-GAD65-related neurologic disorder, malignancy screening is often performed with 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT). Here, we present an interesting image of 18FFDG PET/CT whole body showing muscle uptake and FDG brain showing thalamic hypometabolism in SPS.
Keywords
18F fluorodeoxyglucose positron emission tomography/computed tomography
antiglutamic acid decarboxylase-65
muscle uptake
stiff-person syndrome
A 64-year-old female with diabetes mellitus and hypertension presented with bilateral leg pain and difficulty in walking for the last 1 month. Clinical examination revealed stiff contracted muscle with rigidity in extremities. Blood investigations were normal. With suspicion of stiff-person syndrome (SPS), her antiglutamic acid decarboxylase-65 (GAD65) antibody was elevated. She was referred for 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) to rule out paraneoplastic etiology. Her blood sugar value was 90 mg/dl and was fasting for 6 h before the study. No insulin or dextrose was administered. FDG PET showed intensely hypermetabolic symmetric muscle uptake in the entire body [Figure 1]. No malignancy was detected. FDG brain images in Scenium software showed hypometabolism in bilateral thalamus [Figure 2]. She was started on rituximab 500 mg and has good clinical improvement.
Anti-GAD65 autoantibodies have been identified in SPS, condition causing muscle rigidity and painful spasms.[1] Association with impairment of γ-aminobutyric acid neurotransmission by anti-GAD65 autoantibodies which results in lack of inhibition leadingto relatively hyper-excitable state.[2] FDG PET/CT showing muscle uptake seen in nonfasting state with increased glucose level and due to physiological muscle activity after exercise or walking or pathological uptake in polymyositis are reported.[3] There are case reports of increased muscle uptake in case of insulinoma[4] and Graves’ disease.[5]
O’Toole et al. showed the case of hypermetabolism in muscles in FDG PET/CT in a case of SPS[6] Wang et al.[7] showed 50 cases of whole body FDG showing hypermetabolism in muscles in SPS and 30 cases of brain FDG in same patients showing thalamic hypometabolism.Shoulders and upper limbs were most commonly hypermetabolic followed by hips, lower limbs, and axial musculature. The muscle regions involved correlated with clinical muscle involvement in 42% of individuals. The thalamus exhibited hypometabolism as it is an important component of connecting cortex to striatal network, which are affected in various movement disorders. Our case also showed hypermetabolism in most of muscles and hypometabolism in both thalami. In conclusion, SPS showing muscle uptake can be added to list of pathological muscle uptake in FDG PET/CT.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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