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There are no laboratory markers for the diagnosis of PSP but ocular motor studies, electrophysi-ological studies, MRI, magnetic resonance spectroscopy, and positron emission tomography (PET) scans may be helpful to support the diagnosis or exclude other disorders. In general the sensitivity and specificity of these techniques in distinguishing patients with clinically equivocal or early PSP from other conditions has not been assessed. For this reason this techniques are not yet considered standard diagnostic tools in PSP. The availability and cost of some of these tools also limits their use to research settings for the foreseeable future.

Ocular Motor Studies

Electrooculographic recording may help distinguish PSP patients from other parkinsonian disorders at an early stage (130). There is slight or no saccade impairment in PD and MSA patients with parkinsonism (i.e., those with no cerebellar signs). PSP patients have decreased horizontal saccade amplitude and velocity but normal latency, whereas opposite results are observed in CBD patients. The antisaccade task (looking in the direction opposite to a visual stimulus), which correlates well with frontal lobe dysfunction, is reported to be markedly impaired in patients with PSP, although it may also be impaired in patients with AD. A pilot study suggest that longitudinal electrooculographic studies may help distinguish patients with PSP from those with CBD (131). For further details on the role of electrooculographic studies in the diagnosis of PSP, see Chapter 15.

Neuroimaging

Structural Imaging Changes

CT, as well as MRI, may at some stage in the disease show definite atrophy of the midbrain and of the region around the third ventricle in more than half of PSP patients (132-135) (Figs. 4 A,B). Thinning of the quadrigeminal plate, particularly in its superior part, better seen in sagittal MRI sections, has been shown to support a diagnosis of PSP (Fig. 4C). Minimal signal abnormalities in the periaqueductal region could also be seen in proton density MRI (Fig. 4D). Although CT or MRI of the brain are generally of little help in establishing the diagnosis of PSP, they can aid in ruling out other diagnoses (e.g., CBD when asymmetric atrophy may be present in the parietal area, or MSA when there may be atrophy of the pons, middle cerebellar peduncles, and cerebellum or altered signal intensity in the putamen; it may also be used to rule out multiinfarct states, hydrocephalus, or tumors). See also Chapter 25 for further details on the role of MRI studies in the diagnosis of PSP.

Functional Imaging

Magnetic resonance spectroscopy imaging detects different patterns of cortical and subcortical involvement in PSP, CBD, and PD. PSP patients, compared with controls, have reduced NA/Cre in the brainstem, centrum semiovale, frontal and precentral cortex, and reduced NA/Cho in the lenti-form nucleus. On the other hand, CBD patients, compared with control subjects, have reduced NA/ Cre in the centrum semiovale, and reduced NA/Cho in the lentiform nucleus and parietal cortex. Although significant group differences can be found using this technique, magnetic resonance spec-troscopy is not helpful to differentiate between individual patients.

18F-Fluorodeoxyglucose PET scans and 123IMP-single photon emission computed tomography (SPECT) blood flow studies have both shown marked reduction in frontal and striatal metabolism in PSP. Frontal hypometabolism in PSP is secondary to deafferentation and cortical pathology. However, this finding is not specific to PSP. PET measures of striatal dopamine D2 receptor density using 76Br-bromospiperone, or nC-raclopride are also significantly reduced in most PSP patients, but again, these findings are not specific to PSP. Hypometabolism of glucose in the frontal cortex, and decreased 18F-fluorodopa uptake in the presynaptic nigrostriatal dopaminergic system (with similar reduction in both putamen and caudate) have also been shown by PET in PSP patients. See Chapters 26 and 27 for further details on the role of functional neuroimaging studies in the diagnosis of PSP.

Behavioral and Neuropsychological Evaluations

When evaluated with a series of neuropsychological tests that included the Wisconsin Card Sorting Test, Trail Making Tests, Tower of Hanoi, fluency test, the Similarity and Picture Arrangement subtests of the WAIS-R (Wechsler Adult Intelligence Scale-Revised), motor series of Luria, or imitation behavior, almost all PSP patients examined demonstrate an early and prominent difficulty executive dysfunction (19,20,22,23,26,136) Similarly, the use of the Neuropsychiatric Inventory helps identify the apathy these patients usually manifest (24). Identification of these deficits is helpful for the diagnosis and for the management of these patients. A lack of benefit from levodopa therapy and the presence of severe frontal cognitive and/or behavioral deficits help support the diagnosis of PSP and differentiate this disorder from related disorders as shown in Fig. 5. Consideration of both, patients' response to levodopa and identified deficits in neuropsychological testing not only improves clinicians' diagnostic accuracy but helps us manage these two important aspects of the disease. See Chapters 11-14 for details on the role of neuropsychological studies in the diagnosis of this patient population.

  1. 4. MRI abnormalities in PSP. Midbrain atrophy (A,C), dilation of third ventricle (B), and an increased signal intensity in the periaqueduct gray matter in T2 (D) are the changes typically observed in PSP. Midbrain atrophy measured by an anteroposterior (AP) diameter equal or less than 13.4 mm (135) or an AP diameter equal or less than 17 mm in addition to dilation of third ventricle (132) have been proposed as radiologic features that help distinguish PSP from related parkinsonian disorders, particularly PD and MSA.
  2. 4. MRI abnormalities in PSP. Midbrain atrophy (A,C), dilation of third ventricle (B), and an increased signal intensity in the periaqueduct gray matter in T2 (D) are the changes typically observed in PSP. Midbrain atrophy measured by an anteroposterior (AP) diameter equal or less than 13.4 mm (135) or an AP diameter equal or less than 17 mm in addition to dilation of third ventricle (132) have been proposed as radiologic features that help distinguish PSP from related parkinsonian disorders, particularly PD and MSA.

Neurophysiological Studies

PSP patients have both slowed movement and information processing. Their cognitive slowness can be evaluated with complex reaction time tasks or with cognitive evoked potentials. Event-related brain potentials recorded while PSP patients perform an Oddball task show a normal N1 component but dramatically increased latencies and decreased amplitudes of the P2 and P300 components (137). The remarkably delayed latencies found in PSP have not been reported in any other type of dementia. These findings are different from those reported in CBD (138,139).

Polysomnographic studies show a diminished total sleep time, an increase in awakenings, and progressive loss of REM sleep. These disturbances can be attributed to degeneration of brainstem structures crucial to generate normal sleep patterns, such as the pontine tegmentum, characteristically involved in PSP.

Parkinsonism

Beneficial L-dopa Response i

Poor/Unsustained L-dopa Response

Executive dysfunction

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