The metabolic topography of essential blepharospasm: a focal dystonia with general implications

OBJECTIVE

To determine the metabolic topography of essential blepharospasm (EB).

BACKGROUND

EB is a cranial dystonia of unknown etiology and anatomic localization. The authors have used 18F-fluorodeoxyglucose (FDG) and PET with network analysis to identify distinctive patterns of regional metabolic abnormality associated with idiopathic torsion dystonia (ITD), as well as sleep induction during PET imaging to suppress involuntary movements, thereby reducing this potential confound in the analysis.

METHODS

Six patients with EB and six normal volunteers were scanned with FDG-PET. Scans were performed twice: once in wakefulness and once following sleep induction. The authors used statistical parametric mapping to compare glucose metabolism between patients with EB and control subjects in each condition. They also quantified the expression of the previously identified ITD-related metabolic networks in each subject in both conditions.

RESULTS

With active involuntary movements during wakefulness, the EB group exhibited hypermetabolism of the cerebellum and pons. With movement suppression during sleep, the EB group exhibited superior-medial frontal hypometabolism in a region associated with cortical control of eyelid movement. Network analysis demonstrated a specific metabolic covariance pattern associated with ITD was also expressed in the patients with EB in both the sleep and wake conditions.

CONCLUSION

These findings suggest that the clinical manifestations of EB are associated with abnormal metabolic activity in the pons and cerebellum, whereas the functional substrate of the disorder may be associated with abnormalities in cortical eyelid control regions. Furthermore, ITD-related networks are expressed in patients with EB, suggesting a functional commonality between both forms of primary dystonia.

Dopamine transporter imaging with fluorine-18-FPCIT and PET

Fluorinated N-3-fluoropropyl-2-beta-carboxymethoxy-3-beta-(4-iodophenyl) nortropane (FPCIT) has been synthesized as a dopamine transporter ligand for PET studies. We evaluated the regional brain uptake and the plasma metabolism of [18F]-FPCIT.

METHODS

PET studies were conducted on 7 normal subjects and on 10 patients with Parkinson's disease. After the [18F]-FPCIT injection (4.4+/-1.8 mCi), dynamic scans were acquired over 100 min. Plasma metabolite analysis was performed using high-performance liquid chromatography (HPLC).

RESULTS

Plasma HPLC revealed two peaks corresponding to unmetabolized [18F]-FPCIT and a polar metabolite. The fraction of the parent compound decreased rapidly to 25% at 25 min. Fluorine-18-FPCIT showed a striatum-to-occipital ratio (SOR) of 3.5 at 90 min postinjection. The ratio of striatal-to-occipital distribution volume (DVR) was calculated directly by using a mean tissue-to-plasma efflux constant for occipital cortex obtained in 10 subjects (ki=0.037 min(-1)). DVR measures determined with and without plasma input function were correlated (r=0.98, p < 0.0001). In normal subjects, a significant age-related decline of DVR was observed both for caudate and putamen, corresponding to a 7.7% and 6.4% decline per decade, respectively (r > 0.85, p < 0.01). Both DVR and SOR correctly classified early-stage Parkinson's disease patients with comparable accuracy (p < 0.0001). Age-corrected DVR values correlated negatively with the Uniform Parkinson's Disease Rating Scale composite motor ratings (r=0.66, p < 0.05).

CONCLUSION

The tracer characteristics are compatible with a high-affinity, reversible ligand. FPCIT/PET demonstrated age-related decline in dopamine transporter binding in normal subjects as well as significant reductions in patients with idiopathic Parkinson's disease, which correlates with the disease severity.

False-positive FDG-PET imaging of the thymus of a child with Hodgkin's disease

During the evaluation of a child who had completed treatment for Hodgkin's disease, a PET study strongly suggested recurrent disease in the mediastinum. Biopsies were obtained and revealed normal thymic tissue only, with no evidence of recurrent disease. The ongoing difficulty in establishing accurate disease status in patients treated for Hodgkin's disease is discussed, along with recommendations for treating pediatric patient populations.

Radiosynthesis of [18F] N-3-fluoropropyl-2-beta-carbomethoxy-3-beta-(4-iodophenyl) nortropane and the first human study with positron emission tomography

A procedure for the routine preparation of [18F]FP-CIT has been developed. Purification of the final product was achieved by preparative HPLC using phenethyl column without decomposition or epimerization. [18F] labeled-N-fluoropropyl-2 beta-carbomethoxy-3 beta-(4-iodophenyl) nortropane was prepared and PET imaging was performed on human subjects. A high uptake into striatal regions was observed. HPLC plasma analysis using [18F]FP-CIT indicated the presence of only one metabolite. By directly comparing the behavior of these three radiotracers ([18F]DOPA, [123I]FP-CIT, and [18F]FP-CIT) in the same subjects, we can enhance our understanding of the dopaminergic system as well as the relative potential of these techniques in a clinical research setting.

Bladder wall radiation dose in humans from fluorine-18-FDOPA

PET, in conjunction with 18F-fluorodopa (FDOPA), has become the standard technique to assess basal ganglia degeneration in patients with movement disorders. Based on published dosimetry data, the injected dose of FDOPA is limited to 111 Mbq (3 mCi) because of exposure to the bladder wall, which is the critical organ for such studies. These dosimetry studies are based on mathematical models for the bladder radioactivity accumulation and clearance when the subjects were asked to void approximately 2 hr after the intravenous injection of FDOPA. In this study, we improved the radiation dose estimate to the bladder wall using dynamic PET to image the bladder during the uptake phase as well as before and after voiding.

METHODS

The subjects were tested on a new protocol. They were hydrated preinjection and given a first bladder void break at 40 min postinjection and a second void at the end of study at 120 min.

RESULTS

The MIRD model, applied to the data collected from 10 adults of both sexes, yielded an average absorbed dose of 0.15 +/- 0.08 mGy/MBq (0.57 +/- 0.28 rad/mCi).

CONCLUSION

This absorbed dose is significantly lower than previous estimates and allows for FDOPA injections up to 333 Mbq (9 mCi).

Fluorodopa positron emission tomography with an inhibitor of catechol-O-methyltransferase: effect of the plasma 3-O-methyldopa fraction on data analysis

Flurodopa (FDOPA) is an analogue of L-di-hydroxyphenylalanine (L-dopa) used to assess the nigrostriatal dopamine system in vivo with positron emission tomography (PET). However, FDOPA/PET quantitation is complicated by the presence of the 3-O-methyl-FDOPA (3OMFD) fraction in brain and plasma. Pretreatment with entacapone (OR-611), a peripheral catechol O-methyl-transferase (COMT) inhibitor, greatly reduces the plasma 3OMFD fraction and provides an ideal situation to evaluate the contribution of the plasma 3OMFD fraction in several kinetic models of FDOPA uptake. We performed FDOPA/PET with and without the OR-611 preadministration in six Parkinson's disease (PD) patients. We measured the time-course of the plasma FDOPA and 3OMFD fractions using high-pressure liquid chromatography (HPLC). We calculated striato-occipital ratios (SOR), and estimated the striatal FDOPA uptake rate constant graphically using the plasma FDOPA and occipital tissue time activity curves (KiFD and KiOCC, respectively). We also estimated striatal dopa decarboxylase (DDC) activity (k3D) using a model incorporating independent measurements of 3OMFD transport kinetic rate constants. With the preadministration of OR-611, the pharmacological efficiency in plasma was prolonged significantly (21.1-37.7%; p < 0.01). We also observed significant mean elevations in SOR and KiOCC by 21.8 and 53.5%, respectively (p < 0.05). KiFD and k3D did not show significant change. We conclude that OR-611 prolongs the circulation time of FDOPA in the plasma but does not alter rate constants for striatal FDOPA uptake or decarboxylation.

Combined FDOPA and 3OMFD PET studies in Parkinson's disease

PET has been used to quantify striatal 6-[18F]fluoro-L-dopa (FDOPA) uptake as a measure of presynaptic dopaminergic function. It has been suggested that the estimation of dopa-decarboxylation (DDC) rate, kD3, using a compartmental approach to dynamic FDOPA/PET data, can provide a better objective marker of parkinsonism. This modeling process, however, requires many assumptions to estimate DDC activity with acceptable errors.

METHODS

We combined FDOPA 3-O-methyl-fluorodopa PET studies on three normal subjects and five Parkinson's disease patients.

RESULTS

The contradicted modeling assumptions are: (a) the rate constants across the blood-brain barrier, KD1 and kD2, for 3OMFD and FDOPA were in similar range (ratio approximately equal to 1) and thus not equal to assumed values of KM1/KD1 of 2.3 derived from rat studies and applied to human FDOPA studies and (b) the KD1/kD2 ratio for frontal cortex was not equal to that for the striatum (0.70 +/- 0.15 versus 1.07 +/- 0.3; p < 0.002). Discriminant analyses indicate that simple estimates like the striatum-to-occipital ratio, or the graphically derived unidirectional transport rate constant (KiFD) separate normals from Parkinson's disease patients at least as accurately as estimates of striatal DDC activity (kD3).

CONCLUSION

Measurements of striatal DDC activity with dynamic FDOPA/PET and compartmental modeling may be based on incorrect assumptions. Even though such complex models yield microparameters that may be applicable to certain clinical research demands, they may produce misleading results in other experimental settings.

Early differential diagnosis of Parkinson's disease with 18F-fluorodeoxyglucose and positron emission tomography

Early-stage Parkinson's disease (EPD) is often clinically asymmetric. We used 18F-fluorodeoxyglucose (FDG) and PET to assess whether EPD can be detected by a characteristic pattern of regional metabolic asymmetry. To identify this pattern, we studied 10 EPD (Hoehn and Yahr stage I) patients (mean age 61.1 +/- 11.1 years) using 18F-FDG and PET to calculate regional metabolic rates for glucose. The scaled subprofile model (SSM) was applied to metabolic asymmetry measurements for the combined group of EPD patients and normal subjects to identify a specific covariation pattern that discriminated EPD patients from normal subjects. To determine whether this pattern could be used diagnostically, we studied a subsequent group of five presumptive EPD patients (mean age 50.9 +/- 18.3), five normal subjects (mean age 44.6 +/- 15.3), and nine patients with atypical drug-resistant early-stage parkinsonism (APD) (mean age 44.6 +/- 14.0). In each member of this prospective cohort, we calculated the expression of the EPD-related covariation pattern (subject scores) on a case-by-case basis. We also studied 11 of the EPD patients, five patients with APD, and 10 normal subjects with 18F-fluorodopa (FDOPA) and PET to measure presynaptic nigrostriatal dopaminergic function, and we assessed the accuracy of differential diagnosis with both PET methods using discrimination analysis. SSM analysis disclosed a significant topographic contrast profile characterized by covariate basal ganglia and thalamic asymmetries. Subject scores for this profile accurately discriminated EPD patients from normal subjects and APD patients (p < 0.0001). Group assignments into the normal or parkinsonian categories with FDG/PET were comparable to those achieved with FDOPA/PET, although APD and EPD patients were not differentiable by the latter method. Metabolic brain imaging with FDG/PET may be useful in the differential diagnosis of EPD.

A miniature piezoelectric polymer transducer for in vitro measurement of the dynamic contact stress distribution

Previous studies of contact pressure measurement between articular surfaces have been mostly limited to static techniques. The purpose of our study was to develop a new dynamic technique for a direct measurement of the local contact stresses, and to apply the new method to an in vitro cadaver study of the patellofemoral joint pressures. The miniature transducer consists of a 2 mm diameter and 28 microns thick piece of piezoelectric polymer film sandwiched between two stainless steel electrodes of similar diameter. A water-resistant capsule consisting of Teflon film and Hysol epoxy was applied around the transducer. The transducer was 3 mm in diameter and 0.7 mm in thickness. A 3 mm well was made at six locations in the patella, corresponding to superior, middle, and inferior regions of both facets. Six transducers were cemented within each well, flush with the articular cartilage. The transducers were calibrated in situ before and after the experiment. The femur was rigidly fixed to the loading apparatus and the tibia was allowed to flex and extend through a 90 degrees range of motion using an Instron and a pulley system connected to the quadriceps tendon. Q angles of 0, 5, 10 and 15 degrees were established by adjusting the direction of the quadriceps tendon. Stresses ranging from 0.1-1.3 MPa were recorded at various locations. These values varied in flexion and extension. An overall decrease in these stresses was noted after tuberosity elevation up to 1.5 cm, following which increased values up to 1.8 MPa were recorded mostly in the superior section.(ABSTRACT TRUNCATED AT 250 WORDS)