Imaging Nigrostriatal Dopaminergic Deficit in Holmes Tremor with 18F-PR04.MZ-PET/CT

Analysis of Semiology, Lesion Topography and Treatment Outcomes: A Prospective Study on Post Thalamic Stroke Holmes Tremor

OBJECTIVE

Holmes tremor (HT) comprises rest, postural and intention tremor subtypes, usually involving both proximal and distal musculature. Perturbations of nigro-striatal pathways might be fundamental in the pathogenesis of HT along with cerebello-thalamic connections.

METHODS

Nine patients with an HT phenotype secondary to thalamic stroke were included. Epidemiological and clinical records were obtained. Structural and functional brain imaging were performed with magnetic resonance imaging (MRI) or computed tomography (CT) and positron emission tomography (PET), respectively. Levodopa was administered in sequentially increasing dosage, with various other drugs in case of inadequate response. Longitudinal follow-up was performed for at least three months. The essential tremor rating assessment scale (TETRAS) was used for assessment.

RESULTS

The mean latency from stroke to tremor onset was 50.4 ± 30.60 days (range 21-90 days). Dystonia was the most frequently associated hyperkinetic movement (88.8%). Tremor was bilateral in 22.2% of participants. Clinical response was judged based on a reduction in the TETRAS score by a prefixed value (≥ 30%), pertaining to which 55.5% (n = 5) of subjects were classified as responders and the rest as non-responders. The responders showed improvement with significantly lower doses of levodopa than the remaining nonresponders (240 ± 54.7 mg vs. 400 ± 40.8 mg; p = 0.012).

CONCLUSION

Although levodopa is useful in HT, augmenting the dosage of levodopa beyond a certain point might not benefit patients clinically. Topography of vascular lesions within the thalamus might additionally influence the phenomenology of HT.

Whole-body biodistribution and radiation dosimetry of [18F]PR04.MZ: a new PET radiotracer for clinical management of patients with movement disorders

PURPOSE

[18F]PR04.MZ is a new PET imaging agent for dopamine transporters, providing excellent image quality and allowing for the evaluation of patients with movement disorders such as Parkinson's disease. The objective of this study was to evaluate the biodistribution and radiation dosimetry of [18F]PR04.MZ by serial PET imaging.

METHODS

Six healthy subjects (n = 3 males, n = 3 females) were enrolled in this study. A series of 14 whole-body PET/CT scans were acquired until 5.5 h post-injection of 200 ± 11 MBq of [18F]PR04.MZ. After rigid co-registration, volumes of interest were outlined either on CT or PET images. Time-integrated activity coefficients were calculated for selected source organs. Organ absorbed doses, and the effective dose were calculated using IDAC-Dose 2.1.

RESULTS

Physiological uptake of [18F]PR04.MZ was mainly observed in the striatum, brain, liver, gall bladder, intestine, red marrow and cortical bone. [18F]PR04.MZ was primarily excreted via hepatobiliary clearance and, to a lower extent, via renal clearance. The normalized absorbed doses were highest in gall bladder wall (32.2 ± 6.4 µGy/MBq), urinary bladder wall (27.2 ± 4.5 µGy/MBq), red marrow (26.5 ± 1.4 µGy/MBq), cortical bone surface (26.3 ± 2.5 µGy/MBq), liver (22.5 ± 1.8 µGy/MBq) and kidneys (21.8 ± 1.1 µGy/MBq). The effective dose according to ICRP 60 and 103 was 16.3 ± 1.1 and 16.6 ± 1.5 µSv/MBq, respectively.

CONCLUSION

[18F]PR04.MZ has a favourable dosimetry profile, comparable to those of other 18F-labelled PET tracers, and is suitable for larger clinical applications. Trial registration CEC SSM Oriente, Santiago, Chile, permit 20140520.

[18F]PR04.MZ PET/CT Imaging for Evaluation of Nigrostriatal Neuron Integrity in Patients With Parkinson Disease

INTRODUCTION

Degeneration of dopaminergic, nigrostriatal neurons is the hallmark of Parkinson disease (PD), and PET quantification of dopamine transporters is a widely accepted method for differential diagnosis between idiopathic PD and essential tremor. [18F]PR04.MZ is a new PET tracer with excellent imaging properties allowing for precise quantification of striatal and extrastriatal dopamine transporter. Here we describe our initial experience with [18F]PR04.MZ PET/CT in a larger cohort of healthy controls and PD patients as a proof-of-concept study for this tracer.

METHODS

Eighteen healthy subjects, 19 early PD patients (Hoehn-Yahr I-II), and 13 moderate-advanced PD patients (Hoehn-Yahr III-IV) underwent static PET/CT scans 60 to 90 minutes after injection of 5.16 ± 1.03 mCi (191 ± 38 MBq) [18F]PR04.MZ. Specific binding ratios (SBRs) were calculated for caudate nucleus, anterior putamen, posterior putamen, substantia nigra (SNpc), compared between different groups and correlated with clinical ratings.

RESULTS

[18F]PR04.MZ showed very high and specific uptake in the putamen, caudate, and substantia nigra pars compacta and very low nonspecific binding in other brain regions, and SBR values for the control group were 22.3 ± 4.1, 19.1 ± 3.5, and 5.4 ± 1.2, respectively. A reduction of SBR values was observed in all regions and in both initial and moderate PD, ranging from 35% to 89% (P < 0.001). The observed pattern of reduction was posterior putamen > anterior putamen > substantia nigra pars compacta > caudate, with contralateral posterior putamen being the most affected region. Rostrocaudal depletion gradient was evident in all PD patients and progression correlated with motor manifestations.

CONCLUSIONS

[18F]PR04.MZ PET/CT is a highly sensitive imaging modality for the detection of dopaminergic deficit in nigrostriatal pathways in PD.

Brain 123I-FP-CIT SPECT of a Holmes Tremor Due to Midbrain Pilocytic Astrocytoma

A 24-year-old woman with an unresectable right mesencephalic pilocytic astrocytoma was treated with stereotaxic radiation therapy. Three months after a radiation therapy-induced bleeding, she presented a severe disabling low frequency rest and kinetic tremor involving the left upper limb, associated with dystonia, and a Holmes tremor was suspected. Thereby, we performed a I-FP-CIT SPECT (DATSCAN) that revealed a normal distribution of radiotracer over the left striatum, whereas no binding was seen in the right caudate and putamen. This pattern was consistent with a right severe nigrostriatal dopaminergic denervation due to an ipsilateral red nucleus injury.

Is nigrostriatal dopaminergic deficit necessary for Holmes tremor to develop? The DaTSCAN and IBZM SPECT study

Holmes’s tremor (HT) is assumed to be the result of coexistence of nigrostriatal dopaminergic system impairment and the lesion of cerebello-thalamic pathways. It was suggested that dopaminergic deficiency is responsible for rest tremor, and lack of compensatory cerebellar function leads to spill of tremor into voluntary movements. Cases of HT with and without abnormalities of the presynaptic part of dopaminergic nigrostriatal were published and these findings raised the question of possibility of the postsynaptic lesion. Three patients with HT diagnosed according to criteria of Consensus Statement on Tremor were studied. In all of them SPECT imaging with ligands of presynaptic (I 123-FP CIT—DaTSCAN) and postsynaptic (I 123-iodobenzamide—IBZM) nigrostriatal dopaminergic neurons was performed. Indices of uptake in caudate and putamen normalized to nonspecific uptake in occipital cortex and indices of asymmetry for each whole striatum as well as for putamen and caudate separately were calculated. SPECT studies did not reveal asymmetry of DaTSCAN and IBZM binding in striatum in all studied subjects. The current clinical diagnostic criteria of HT are presumably insufficiently specific and when using them we identify patients both with and without the involvement of dopaminergic system. These two groups may represent tremor disorders of similar phenomenology but of different pathomechanism.