Introduction

Primary progressive aphasia (PPA) without generalized dementia, first reported by Mesulam in 1982 [9], is a syndrome of language disorders lasting more than 2 years with preservation of activities of daily living and relative sparing of non-verbal cognitive abilities [10]. The pathology is variable and comprises several different degenerative conditions, including Alzheimer's disease [6], Pick's disease with Pick bodies [5, 12], Creutzfeldt-Jacob disease [8], corticobasal degeneration [7], and "nonspecific focal atrophy" [10], all of which are usually associated with cortical atrophy and hypometabolism around the left perisylvian area concerning language networking. We report the first autopsy case of an elderly man presenting with an 8-year history of PPA, who was diagnosed with progressive supranuclear palsy (PSP) based on neuro-glial tau pathology. Cortical pathology accentuated in the left precentral area may have contributed to PPA.

Case report

The patient was a right-handed male who retired at age 54 from school teaching. No family history of dementia, parkinsonism, or other neurological illness suggestive of motor neuron disease was reported. At age 64, he noticed difficulty in speaking over the telephone. His vocabulary was reduced and usage of postpositional particles became awkward, but he could understand conversations, repeat words, and read silently. At age 67, neuropsychological testing in our hospital revealed an IQ of 124 (verbal IQ; 127, performance IQ; 117) on the Wechsler Adult Intelligence Scale-Revised (WAIS-R) and an IQ of 110 on the Kohs' Block Design Test. However, his score was 161/165 for the Token test and occasional paraphasia and literal paragraphia on dictation and slight decrease in the recall of animal names were observed on the Western Aphasia Battery test. His non-fluent language condition was considered mild motor aphasia. Neurologically, there were no abnormalities in the motor, sensory, oculomotor, or cerebellar systems, including apraxia, bulbar or pseudobulbar palsy, and frontal release signs. There were no frontal lobe features, such as personality change, apathy, and disinhibition. Brain T2-weighted magnetic resonance imaging (MRI) showed mild enlargement of the sylvian fissure and a high intensity lesion in the white matter on the left (Fig. 1A). Cerebral angiography revealed no atherosclerotic change. At age 71, his speech gradually slowed, with spaces between words, although his IQ was 124 (verbal IQ; 123, performance IQ; 122) on the WAIS-R. At age 73, he developed clumsiness with the right hand and dysphagia. Deep tendon reflexes were mildly hyperactive and the palmomental reflex became positive. Brain T2-weighted MRI revealed apparent progression of left frontal lobe atrophy (Fig. 1B). At age 74, repetitive behavior and postural instability became evident before his death from influenza pneumonia in Hatsuishi hospital. Permission for autopsy was obtained from his relatives.

Fig. 1.
figure 1

Coronal sections of T2-weighted magnetic resonance imaging at age 67 (A) and 73 (B), 3 and 9 years from primary progressive aphasia onset, respectively. The left frontal lobe atrophy apparently progressed over the 6 years in association with the enlargement of the sylvian fissure, the anterior horn of the lateral ventricle on the left side (L), and the third ventricle. In contrast, the temporal lobe and the inferior horn of the lateral ventricle had no remarkable change in size

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Methods

The left hemisphere was fixed in formalin, then embedded in paraffin. Serial coronal sections of the brain were examined macroscopically. Sections were stained using hematoxylin-eosin (HE), Klüver-Barrera, and modified Bielschowsky and Gallyas-Braak methods for histological examination. Monoclonal anti-phosphorylated tau antibody (AT8; Innogenetics, Ghent, Belgium; 1:1,000) was used as the primary antibody for immunohistochemistry. Sections were deparaffinized and incubated with primary antibodies overnight at 4°C, then visualized by the avidin-biotin-peroxidase complex method using diaminobenzidine tetrahydrochloride as the chromogen.

Sarkosyl-insoluble tau was extracted from the frontal cortex in the right side as described previously [4]. The sample was then dephosphorylated by incubation with E. coli alkaline phosphatase (type III; Sigma Fine Chemicals) [4]. All six isoforms of recombinant human tau protein were expressed in E. coli BL21 (DE3) [3] and were used as control samples. Dephosphorylated and nondephosphorylated samples in addition to a mixture of six isoforms of recombinant tau were loaded on 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and blotted onto a polyvinylidine-difluoride membrane (Millipore Co., USA). Membranes were incubated overnight with HT7, a phosphorylation-independent monoclonal antibody to tau (Innogenetics, Belgium). Following incubation with a biotinylated secondary antibody, labeling was detected using Vectastatin ABC-AP kit (Vector Laboratory, USA) with 5-bromo-4-chloro-3-indolylphosphate p-toluidine salt and nitroblue tetrazolium chloride as the chromogen.

Results

The brain weighed 1,265 g. The cerebral hemisphere displayed moderate cortical atrophy of the frontal lobe, including the precentral gyrus, particularly in the left side. The basal ganglia, including the subthalamic nucleus, were unremarkable. The substantia nigra showed mild loss of pigmentation. The brain stem and cerebellum were unremarkable.

Microscopical examination revealed a high frequency of neurofibrillary tangles in the subcortical regions, including the thalamus (Fig. 2B), subthalamic nucleus (Fig. 2A), substantia nigra, oculomotor nuclei, locus ceruleus, pontine nuclei (Fig. 2C), pontine tegmentum, and inferior olivary nucleus (Fig. 2D). Mild neuronal loss and gliosis was also apparent in the globus pallidus, substantia nigra, subthalamic nucleus, thalamus, and red nucleus. Tau-positive argyrophilic inclusions, including tuft-shaped astrocytes and oligodendroglial coiled bodies, were present mainly in the striatum, subthalamic nucleus (Fig. 2A) and thalamus (Fig. 2B). The cerebellar dentate nucleus displayed grumose degeneration. Cerebral cortical neuronal loss and gliosis was mild, but neurofibrillary tangles were frequently found in the frontal cortex. These findings were particularly pronounced in the premotor and motor cortices, including pars opercularis, where mild microvacuolar change with mild to moderate neuronal loss and gliosis was obvious and the arrangement of the cortical layer became obscure (Fig. 3A). Moreover, many tuft-shaped astrocytes were present in the cortex (Fig. 3A, B) and numerous argyrophilic threads were also present from the deeper layers of the cortex to the underlying subcortical white matter (Fig. 3C). The pyramidal tract at the medulla oblongata showed moderate degeneration with gliosis, although Betz cells were relatively preserved. No astrocytic plaques or ballooned neurons, which would have been suggestive of corticobasal degeneration, were observed in the cerebral cortex. No infarcts were present in the brain, including the white matter of the frontal lobe. In view of the tau-positive and argyrophilic neuro-glial pathology in the cortical and subcortical structures and grumose degeneration described above, PSP was diagnosed [2].

Fig. 2.
figure 2

Neuropathological findings in the subcortical and brain stem structures. Tau-positive and argyrophilic neurofibrillary tangles (large arrows), tuft-shaped astrocytes (arrowheads), and oligodendroglial coiled bodies (small arrows) appeared in the subthalamic nucleus (A), the thalamus (B), the pontine base (C) and the inferior olivary nucleus (D). A, C, D Tau immunostaining and HE stain. B Gallyas-Braak method and HE stain. A ×168, B ×96, C ×94, D x240

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Fig. 3.
figure 3

Neuropathological findings in the frontal cortex. A Mild microvacuolar degeneration and disarrangement of layers in the superficial layers of motor cortex associated with many neurofibrillary tangles (arrowheads) and glial tangles (arrows). B Neurofibrillary tangle (arrowhead) and tuft-shaped astrocytes (arrow). C Numerous argyrophilic threads associated with oligodendroglial coiled bodies (arrow) in the underlying subcortical white matter. A–C Gallyas-Braak method and HE stain. A ×72, B ×146, C ×395

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Immunoblotting with HT7 revealed that sarkosyl-insoluble tau appeared as two major bands of 68 and 64 kDa (Fig. 4, lane 1). After alkaline phosphatase treatment of sarkosyl-insoluble materials, tau appeared as two major bands corresponding to four repeat tau isoforms with 0 and 29 amino acid inserts in the N-terminal region (4R0N and 4R29N) (Fig. 4, lane 2). These findings are consistent with PSP [11].

Fig. 4.
figure 4

Immunoblot of sarkosyl-insoluble tau stained with HT7. Nondephosphorylated tau migrates as two major bands of 68 and 64 kDa (lane 1). Dephosphorylation reveals two major bands that align with recombinant tau isoforms of four microtubule-binding repeats (referred to as 4R) with 0 and 29 amino acid inserts in the N-terminal region (4R0N and 4R29N) (lane 2). The six recombinant human tau isoforms are shown in lanes 3

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Discussion

PSP is typically characterized clinically by postural instability leading to falls, gait disturbance, and supranuclear gaze palsy, and pathologically by neuro-glial tau pathology in subcortical and brain stem structures such as the substantia nigra, subthalamic nucleus, globus pallidus, oculomotor nuclei, pontine nucleus, and inferior olivary nucleus [2]. Early studies emphasized the lack of neocortical pathology in PSP, but more recent studies, particularly using the Gallyas-Braak method, indicate less pronounced but consistent involvement of the frontal lobe, possibly accounting for concrete thought and impaired attention [2]. Our case displayed slowly progressive non-fluent aphasia without generalized dementia over 8 years from onset, compatible with the criteria for PPA [9, 10]. Finally, in the 2 years prior to his death, the development of behavioral abnormality, postural instability, and dysphagia were suggestive of the frontal lobe symptoms and motor dysfunction frequently found in PSP. PPA was correlated with a focal cortical dysfunction due to left frontal lobe atrophy on MRI, and, on the basis of pathological findings in our case, was attributed to the tau pathology of PSP accentuated in the left precentral area. The lack of supranuclear gaze palsy and other motor symptoms that developed at the end of the clinical course are consistent with relatively mild neuronal changes in the subcortical and brain stem structures.

It is unclear in our case what determined the site predominance, cortical or subcortical pathology. However, PSP with cortical pathology reportedly displays later onset of subcortical symptoms than cortical symptoms, later onset age and longer disease duration than PSP without cortical pathology [1]. Furthermore, the case of a 78-year-old man presenting with a 6-year history of PPA has been reported in which a pathological diagnosis of PSP was considered more likely due to glial tauopathy in the motor cortex [13]. This was similar to our case, although without any subcortical pathology or typical clinical features. An atypical elderly PSP may therefore exist in which cortical pathology initially develops and slowly progresses with or without subsequent subcortical pathology. Further investigation is needed to clarify this; however, we should bear in mind that cortical pathology of PSP, particularly in the frontal lobe, could cause focal cortical symptoms consistent with PPA. We emphasize that PSP should be differentiated from degenerative conditions presenting with PPA.