We describe the phenomenon of crossed cerebellar diaschisis (CCD) in four subjects diagnosed with Alzheimer's disease (AD) according to the National Institute on Aging -Alzheimer Association (NIA-AA) criteria, in combination with 18F-FDG PET and 11C-PiB PET imaging. 18F-FDG PET showed a pattern of cerebral metabolism with relative decrease most prominent in the frontal-parietal cortex of the left hemisphere and crossed hypometabolism of the right cerebellum. 11C-PiB PET showed symmetrical amyloid accumulation, but a lower relative tracer delivery (a surrogate of relative cerebral blood flow) in the left hemisphere. CCD is the phenomenon of unilateral cerebellar hypometabolism as a remote effect of supratentorial dysfunction of the brain in the contralateral hemisphere. The mechanism implies the involvement of the cortico-ponto-cerebellar fibers. The pathophysiology is thought to have a functional or reversible basis but can also reflect in secondary morphologic change. CCD is a well-recognized phenomenon, since the development of new imaging techniques, although scarcely described in neurodegenerative dementias. To our knowledge this is the first report describing CCD in AD subjects with documentation of both 18F-FDG PET and 11C-PiB PET imaging. CCD in our subjects was explained on a functional basis due to neurodegenerative pathology in the left hemisphere. There was no structural lesion and the symmetric amyloid accumulation did not correspond with the unilateral metabolic impairment. This suggests that CCD might be caused by non-amyloid neurodegeneration. The pathophysiological mechanism, clinical relevance and therapeutic implications of CCD and the role of the cerebellum in AD need further investigation.
4-[123I]Iodo-N-[2-[4-(6-trifluoromethyl-2-pyridinyl)-1-piperazinyl]ethyl]benzamide (1.123I), a potential SPECT 5-HT(1A) radioligand, was evaluated in vivo in rats. Biodistribution studies were performed leading to a % ID in the brain of 0.22 at 5 min p.i. No significant differences in % ID/g tissue of the different isolated brain regions (hippocampus, hypothalamus, striatum, cortex and cerebellum) could be demonstrated. Blocking experiments with 8-OH-DPAT, WAY100635 and ketanserin could not show any significant change in tracer uptake in the isolated brain regions. These data suggest that uptake in the brain does not represent binding of 1.123I to the 5-HT(1A) receptor.
Studies of serotonin metabolites in body fluids in attempted suicide patients and of post-mortem brain tissue of suicide victims have demonstrated the involvement of the serotonergic neurotransmission system in the pathogenesis of suicidal behaviour. Recently developed neuroimaging techniques offer the unique possibility of investigating in vivo the functional characteristics of this system. In this study the 5-HT2a receptor population of patients who had recently attempted suicide was studied by means of the highly specific radio-iodinated 5-HT2a receptor antagonist 4-amino-N-[1-[3-(4-fluorophenoxy) propyl]-4-methyl-4-piperidinyl]-5-iodo-2-methoxybenzamide or 123I-5-I-R91150. Nine patients who had recently (1-7 days) attempted suicide and 12 age-matched healthy controls received an intravenous injection of 185 MBq 123I-5-I-R91150 and were scanned with high-resolution brain single-photon emission tomography (SPET). Stereotactic realigned images were analysed semi-quantitatively using predefined volumes of interest. Serotonin binding capacity was expressed as the ratio of specific to non-specific activity. The cerebellum was used as a measure of non-specific activity. An age-dependent 5-HT2a binding index was found, in agreement with previous literature. Deliberate self-harm patients had a significantly reduced mean frontal binding index after correction for age (P=0.002) when compared with controls. The reduction was more pronounced among deliberate self-injury patients (DSI) (P<0.001) than among deliberate self-poisoning patients (DSP). Frontal binding index was significantly lower in DSI patients than in DSP suicide attempters (P<0.001). It is concluded that brain SPET of the 5-HT2a serotonin receptor system in attempted suicide patients who are free of drugs influencing the serotonergic system shows in vivo evidence of a decreased frontal binding index of the 5-HT2a receptor, indicating a decrease in the number and/or in the binding affinity of 5-HT2a receptors.
In longitudinal brain studies of dementia of the Alzheimer type (DAT), the cerebellum is often used as a reference region for single photon emission computed tomography (SPECT) quantification, which assumes no significant regional influence of physiological fluctuations or pathology. With the use of absolute quantification in DAT patients, reproducibility of cerebellar uptake of technetium-99m-d,l-hexamethylpropyleneamine oxime (HMPAO) was tested and compared with the mean absolute cerebellar tracer uptake value in DAT patients and healthy control subjects. In 13 DAT patients SPECT studies were repeated within 2 weeks to assess reproducibility of cerebellar regional brain uptake (rBU). With calibrated point sources as scaling factors, cerebellar activity was expressed as rBU of HMPAO per cm3 brain tissue in percent of the injected lipophilic dose of 740 MBq (20 mCi). Also, mean cerebellar rBU in patients suffering from DAT was calculated and compared with a previously established database obtained in healthy volunteers. Repeated SPECT studies within a 2-week interval in clinically stable patients resulted in a mean rBU increase of 6.8 +/- 10.3% in the second SPECT study as compared with the first. A similar shift was previously reported in healthy volunteers. Mean cortical cerebellar rBU values in DAT patients and in the healthy reference population concurred, after cumulative corrections for body surface and for a mean brain volume of 1350 ml (obtained in healthy control subjects), showing respective mean values of 53.9 +/- 7.4 and of 52.0 +/- 7.3 x 10(-6) of the injected lipophilic dose 740 MBq (20 mCi) of HMPAO per cm3 of brain tissue. A unidirectional shift in mean absolute cerebellar uptake values occurs between repeat SPECT examinations in DAT patients similar to previous findings in a group of healthy volunteers. The origin of this phenomenon remains elusive but deserves further study with regard to SPECT (semi)quantification in DAT patients. Most interestingly, the presented findings suggest that with the use of HMPAO SPECT in DAT patients the cerebellum remains scintigraphically uninvolved.
A 73-year-old right-handed man with ischemic infarction in the vascular territory of the right arteria cerebellaris superior is described. In the acute phase he presented with cerebellar and brainstem symptoms, followed within a few days by a paresis of the right arm and unexpected language disturbances of aphasic origin. The core features of the aphasic syndrome corresponded to a diagnosis of Luria's dynamic aphasia, complicated by expressive and receptive agrammatism. During one year follow-up the ataxia and paretic symptoms disappeared but the slightly ameliorated aphasic syndrome and the sensory disturbances in the left hemicorpus persisted. In the absence of any neuroradiological evidence for a structural lesion in the left frontal language areas, the hypothetical causative role of the right cerebellar lesion on the contralateral prefrontal aphasic symptomatology is advocated and supported by positive 99mTc-hexamethylpropyleneamine oxime single-photon emission-computed tomography findings, revealing a focal hypoperfusion in the clinically suspected areas. In our case, this phenomenon of so-called 'crossed cerebello-cerebral diaschisis', reflecting the distant functional impact of the right cerebellum on the contralateral prefrontal cortical areas, is for the first time associated with an aphasiologic substrate. The co-occurrence of a right cerebellar lesion and an aphasic syndrome forms the first clinical illustration of the pathophysiological hypothesis of a deactivation of prefrontal left hemisphere language functions due to the loss of excitatory impulses through cerebello-ponto-thalamo-cortical pathways.
[(11)C]-PK11195 PET has been used for in vivo brain imaging of microglia activation in Parkinson's disease (PD) patients. COX-2 inhibition has been shown to reduce neuroinflammation and neurodegeneration in animal models of PD. This pilot study assessed the use of [(11)C]-PK11195 PET to quantify neuroinflammation and evaluate the ability of COX-2 inhibition to reduce neuroinflammation in PD patients. Fourteen PD patients and eight healthy, age matched controls underwent a [(11)C]-PK11195 PET and MRI scan. Five PD patients were scanned before and after one month of celecoxib treatment 200 mg/day. Arterial plasma sampling and metabolite analysis were performed to create plasma input curves. A 2-compartment model and Logan analysis were applied and parametric DV images were compared using t-test in SPM2. In addition a simplified reference region model (SRTM) was applied, with both the cerebellum and a reference region derived from cluster analysis. Using the cluster analysis, PD patients showed higher contralateral putamen BP and midbrain BP compared to controls, although considerable overlap was seen and differences were not statistically significant. Unexpectedly, BP and DV after celecoxib were slightly higher. Cerebellum as reference region resulted in lower BP values and k(3)/k(4) gave 10-fold higher BP values. Linearization of the data did not show differences between PD patients and controls. In current practice, [(11)C]-PK11195 seems an unsuitable tracer for accurate or reliable quantification of neuroinflammation. Refinement of [(11)C]-PK11195 uptake analysis and, more importantly, further development of better tracers is necessary to enable accurate measurement of neuroinflammation and effects of anti-inflammatory treatment in patients.