Argyrophilic Grain Disease Clinically Presenting as Progressive Supranuclear Palsy with Progressive Gait Freezing

Abstract

Background

Argyrophilic grain disease (AGD) is a four‐repeat tauopathy characterized by the accumulation of argyrophilic grains. Its primary clinical manifestation is late‐onset amnestic dementia. While the extension of argyrophilic grains to the substantia nigra may be related to its potential association with parkinsonism, biochemical analyses are lacking.

Objectives

To elucidate the extent of AGD to the midbrain, including the substantia nigra, using histopathological examination and biochemical analysis in a pathologically proven case of AGD presenting with parkinsonism and cognitive impairment.

Methods

We describe the case of a patient suggestive of progressive supranuclear palsy. Neuropathological and biochemical investigations were performed.

Results

Neurological examination of an 80‐year‐old man with a 6‐year history of gait disturbance revealed parkinsonism, including gait freezing, postural instability, bradykinesia, and cognitive impairment. The patient was diagnosed with progressive supranuclear palsy with progressive gait freezing. Five years later, the patient reported falling backward repeatedly, became wheelchair‐bound, and died of pneumonia. Macroscopic observations revealed marked amygdala atrophy. Microscopic findings revealed argyrophilic grains in the limbic system, compatible with Saito stage III, as well as in the substantia nigra and midbrain tegmentum. Western blotting showed an AGD‐specific band pattern, and immunoelectron microscopy analyses showed an AGD‐specific tau filament of abnormally phosphorylated tau in both the nucleus accumbens and midbrain.

Conclusions

This report further confirmed that AGD presents with parkinsonism, commensurate with AGD pathology and biochemical findings extending to the midbrain. Therefore, AGD should be considered in the differential diagnosis of cases presenting with parkinsonism and cognitive impairment in the older population.

Case Report

Argyrophilic grain (AG) is a four‐repeat tauopathy characterized by the accumulation of comma‐ or spindle‐shaped argyrophilic grains with phosphorylated tau immunoreactive pretangles and granular fuzzy astrocytes, and the state is referred to as AG disease (AGD) when AGs are observed in the central nervous system, particularly in the limbic system. ¹ , ² , ³ , ⁴ Saito et al proposed a propagation paradigm for AGD that starts in the ambient gyrus (stage I), spreads to the medial temporal lobe (stage II), reaches the basal forebrain and cingulate gyrus (stage III), and is associated with dementia in later stages. ² AGD shows specific band patterns in western blotting that mimic corticobasal degeneration (CBD) but are distinguished from progressive supranuclear palsy (PSP) ⁵ , ⁶ , ⁷ by the presence of specific tau filaments identified through immunoelectron microscopy ⁵ , ⁶ , ⁷ and cryo‐electron microscopy (EM) studies, which differentiate AGD from other four‐repeat tauopathies, including CBD and PSP. ⁸ In vivo, neuroimaging has shown atrophy of the medial temporal lobe, often with laterality on magnetic resonance imaging (MRI), ³ , ⁹ which is accompanied by decreased uptake on ¹⁸F‐labeled fluorodeoxyglucose positron emission tomography (FDG‐PET). ³

The clinical manifestation of the first report of AGD was late‐onset, slowly progressive amnestic dementia. ¹ , ² Although it usually accompanies other comorbid pathologies, our previous study involving 50 cases of the 1241 consecutive autopsy series found that AGD was the sole pathology to explain the dementia. ² Later, an association between AGD and psychiatric symptoms was also identified. ⁴ Furthermore, several case reports and cohort studies have suggested the association of AGD with parkinsonism. ⁵ , ⁶ , ¹⁰ , ¹¹ , ¹² , ¹³ The extension of AGs into the substantia nigra has been suggested to contribute to parkinsonism. ⁵ , ⁶ However, this finding is based on morphological findings alone and is not supported by biochemical analyses of the brainstem. In this report, we describe the clinical symptoms and radiological findings of a patient with progressive supranuclear palsy (PSP). The primary neuropathology was AGD of the limbic system, which extended to the midbrain. Western blotting and immuno‐EM analysis of the nucleus accumbens and midbrain showed AGD‐specific band patterns and tau filaments, respectively, which differ from those observed in PSP.

The patient in the present case, an 80‐year‐old man, was admitted to our hospital with gait and memory disturbances. He first experienced symptoms at 74 years of age when he fell and was temporarily unable to walk without assistance due to gait freezing. At 79 years of age, the patient became forgetful and occasionally failed to clean up the restroom after using it. In addition, the patient's facial expressions were diminished, and he was described as “quick to anger” and “less likely to laugh” by his family members. The Hasegawa Dementia Scale‐Revised (HDS‐R) score was 18/30. Neurological examination revealed gait freezing, postural instability, a slightly impaired upward gaze, and bradykinesia. No tremors or rigidity and no neck extension or Babinski sign were observed. Urinary incontinence was noted, but no constipation was observed. Brain MRI showed severe atrophy of the amygdala, predominantly on the right side (Fig. 1A), and volume loss of the midbrain tegmentum (83 mm² < 101–169 mm²) ¹⁴ (Fig. 1B). Dopamine transporter single‐photon emission computed tomography with ¹²³I‐ioflupane (DaT SPECT) revealed decreased dopamine uptake in the putamen (Fig. 1C). The specific left and right binding ratios were 1.98 and 2.07, respectively. FDG‐PET showed severe hypometabolism in the limbic system, with a right predominance (Fig. 1D,E). No increased uptake of ¹¹C‐Pittsburgh compound on B amyloid PET (PiB‐PET) was observed (Fig. 1F). Cerebrospinal fluid (CSF) levels of total tau, phosphorylated tau, and amyloidβ_1‐42 were all within normal limits, at 171.7 (<300.0), 25 (<55.0), and 544.6 (>500.0) pg/mL, respectively.

Figure 1.

Imaging findings of the case. MRI: severe, predominantly right‐side amygdala atrophy in addition to temporal and frontal lobe atrophy (A). Midbrain tegmentum atrophy (B). DaT SPECT with ¹²³I‐ioflupane: bilaterally decreased striatum uptake (C). ¹⁸F‐FDG‐PET: predominantly right‐side severe hypometabolism in the medial temporal (arrows) (D, E). PiB‐PET: no amyloid β deposition (F). DaT SPECT, Dopamine transporter single‐photon emission computed tomography with ¹²³I‐ioflupane; MR, Magnetic resonance imaging; ¹⁸F‐FDG‐PET, ¹⁸F‐labeled fluorodeoxyglucose positron emission tomography; PiB‐PET, ¹¹C‐Pittsburgh compound on B amyloid photon emission computed tomography;

The patient was diagnosed with possible PSP with progressive gait freezing based on the clinical diagnostic criteria from the Movement Disorder Society. ¹⁵ L‐dopa was prescribed at up to 300 mg/day, with minimal subjective improvement. At 82 years of age, the patient's emails lost their sentence structure because of typing errors. The patient also experienced repeated backward falls with freezing; he could not climb stairs at home, and his spontaneous speech decreased. At 85 years of age, the patient's bradykinesia worsened with rigidity or gegenhalten of no laterality. Dysphagia and difficulties in writing were also observed. The patient required wheelchair use. The HDS‐R and Mini‐Mental State Examination scores were 16/30 and 21/30 with delayed recall scores of 1/6 and 0/3, respectively. The patient died of aspiration pneumonia at the same age. The total duration of parkinsonism was 11 years, and that of dementia was 5 years. No family history of parkinsonism or dementia was evident.

Pathological Findings

After obtaining consent from the patient's family, an autopsy was performed 9 h and 37 min after death. Postmortem neuropathological examination was performed according to the Brain Bank for Aging Research Protocol. ² , ³ , ⁵ , ⁶ The brain weighed 1309 g. Marked atrophy of the amygdala was observed, particularly on the right side (Fig. 2A). The hippocampus showed atrophy with anterior dominance. Atrophy of the subthalamic nucleus was not conspicuous (Fig. 2B). A horizontal section of the brainstem showed mild depigmentation of the substantia nigra (Fig. 2C) and preserved locus coeruleus (Fig. 2D). Histological examination revealed neuronal loss and gliosis in the amygdala and ambient gyrus (Fig. 2E). Abundant AGs were observed in the ambient gyrus (Fig. 2F), amygdala, temporal pole, and insula along with pretangles and granular fuzzy astrocytes (Fig. 2G), compatible with Saito stage III. The number of neurons containing melanin in the substantia nigra pars compacta was slightly decreased (Fig. 2H,I). In addition, AGs, four‐repeat tau positive granular fuzzy astrocytes, and pretangles were present in the substantia nigra (Fig. 2J–N), superior colliculus, and periaqueductal gray matter. Anti‐dopamine transporter immunostaining revealed decreased immunoreactivity in this case compared to the normal control (Fig. 2O: this case, Fig. 2P: control). Atrophy or neuronal loss was not conspicuous, including in the subthalamic nuclei (Fig. 2Q,R). A few pretangles and granular fuzzy astrocytes were evident in the subthalamic nucleus (Fig. 2S,T), putamen, and caudate nucleus but not neuronal loss. Table S1 presents the distributions of AGs, pretangles, granular fuzzy astrocytes, and neuronal loss. AGs were not present in the neocortex. Tufted astrocytes, astrocytic plaques, and globular glial inclusions were not observed.

Figure 2.

Neuropathological findings. Macroscopic examination revealing severe amygdala and ambient gyrus atrophy (A). Atrophy of the subthalamic nucleus (arrow) is not conspicuous (B). Mild substantia nigra depigmentation (C). Inconspicuous locus coeruleus depigmentation (D). Ambient gyrus showing neuronal loss with vacuolation in the superficial layer (E) with many argyrophilic grains (F). Pretangles and granular fuzzy astrocytes in the amygdala in phosphorylated tau immunostaining (clone AT8; mouse monoclonal; Innogenetics, Ghent, Belgium; 1:4000) (G). Neuronal loss in the substantia nigra (H, I) with gliosis and scattered melanin‐containing phagocytes (right‐upper inset) and some positivity for anti‐four‐repeat tau antibody staining (RD4, clone 1E1/A6, mouse monoclonal; Upstate, Lake Placid, NY, USA 1:200) (right‐lower inset) (I). Grains and granular fuzzy astrocytes in the substantia nigra (J). Argyrophilic grains (K) are 4R‐tau immunoreactive (L) in the substantia nigra with pretangles in melanin‐containing neurons (M) and granular fuzzy astrocytes (N). Anti‐dopamine transporter immunostaining (rabbit monoclonal; Abcam, Tokyo, Japan; 1:250) showing decreased immunoreactivity (O) in this case compared to the normal control (P). Atrophy or neuronal loss is not evident in the subthalamic nucleus (Q, R). A small number of granular‐fuzzy astrocytes (S) and pretangles (T) are observed. Scale bars: (A): 2 cm, (B): 1 cm, (C, D): 5 mm, (E, F): 250 μm，(G, I, J): 100 μm, (H): 200 μm, (K, L): 10 μm, (M, N, T): 20 μm, (O, P): 2 mm, (Q): 1 mm, (R, S): 50 μm, Inset: (F): 10 μm, (G): 20 μm, (I): 50 μm (upper), 20 μm(lower). Staining: (E, I, R) hematoxylin and eosin (HE) staining; (F, K) Gallyas staining; (H, Q) Kleuver‐Barrera staining; (G, J, S, T) AT8 immunostaining; (L, M, N) (I: inset) RD4 immunostaining; (O, P) anti‐dopamine transporter immunostaining.

A few cored and diffuse plaques were observed in the frontal, parietal, and temporal cortices, indicating Thal Stage 1 and Consortium to Establish a Registry for Alzheimer's Disease (CERAD) A. Neurofibrillary tangles (NFTs) were observed in the transentorhinal and entorhinal cortices, compatible with Braak NFT stage II (ABC score: A1B1C1). No LB pathologies were observed. Only a small number of TAR DNA‐binding protein 43 (TDP‐43) immunoreactive neuronal cytoplasmic inclusions with dystrophic neurites were observed in the hippocampal uncus but not in the brainstem, including the substantia nigra (limbic‐predominant age‐related TDP‐43 encephalopathy neuropathological change: LATE‐NC stage 1b). Vascular lesions were not observed, and neither amyloid angiopathy nor arteriosclerosis was conspicuous.

Biochemical analyses were performed as previously described. ⁷ Western blot analysis of sarkosyl‐insoluble fractions of the frozen specimens of the nucleus accumbens and midbrain showed a predominant doublet band of 37 kDa corresponding to C‐terminal tau, in addition to the 64‐kDa and 68‐kDa bands corresponding to full‐length tau, compatible with AGD, which mimics CBD but is distinct from PSP ⁷ (Fig. 3A–D). Furthermore, immuno‐EM showed tau C‐positive ribbon‐like tau filaments consistent with AGD but different from CBD in both anatomical lesions ⁷ (Fig. 3E,F).

Figure 3.

Western blotting and immunoelectron microscopy of phosphorylated tau in sarkosyl‐insoluble fractions. Western blot using anti‐tau antibody (clone T46) showing 64‐ and 68‐kDa (full‐length tau) and two ~37‐kDa (C‐terminal tau) bands in the nucleus accumbens (A) and midbrain (B), similar to corticobasal degeneration (C) and different from progressive supranuclear palsy (D), with 33‐kDa bands. Immuno‐EM showing anti‐tau antibody (clone tau C) positive ribbon‐like tau filaments in the nucleus accumbens (E) and midbrain (F). Scalebar: 50 nm. EM, cryo‐electron microscopy.

Discussion

This is the first case to demonstrate AGD pathology in the midbrain using both morphological examination and biochemical analysis in a patient clinically diagnosed with PSP with progressive gait freezing. For clinical diagnosis, gait freezing within 3 years of onset is a core clinical feature of PSP, with progressive gait freezing defined by the clinical diagnostic criteria from the Movement Disorder Society. Atrophy of the midbrain tegmentum on brain MRI and reduced dopamine transporter uptake on DaT SPECT are supportive imaging findings of PSP. In contrast, memory disturbances and a slowly progressive disease course are suggestive of AGD. On brain MRI, right‐dominant bilateral atrophy of the anterior limbic system and decreased uptake in the medial temporal lobe on FDG‐PET are supportive imaging findings of AGD. ³ , ⁹ Neuropathological examination and biochemical analysis led to the diagnosis of AGD in the present case. Moreover, no PSP pathologies were observed.

Several cases clinically diagnosed with PSP or dementia with Lewy bodies (DLB) have turned out to be AGD on neuropathological examination. ⁵ , ⁶ , ¹⁰ , ¹¹ Several cohort‐based studies have also suggested an association between AGD and parkinsonism, including gait disturbance. ¹² , ¹³ However, detailed clinical, radiological, and neuropathological examinations have not been performed. Recently, Arakawa et al reported AGs, pretangles, and granular fuzzy astrocytes in the substantia nigra in a patient with AGD clinically diagnosed with PSP, ⁵ compatible with probable PSP with Richardson's syndrome. The present case further widens the clinical spectrum of AGD presenting with parkinsonism to the point of showing predominant gait freezing.

Among AGD cases presenting with parkinsonism, corticobasal syndrome has not been described. This might be explained by the distribution of AGD in the aged cohort, which extends to the brainstem but not to the neocortex and is responsible for disease‐specific syndromes, including apraxia, alien limb phenomena, and cortical sensory loss.

Regarding CSF examination, in the present case, the total and phosphorylated tau levels were within the normal ranges, similar to those in the case presented by Arakawa et al ⁵ (total tau: 90.8 pg/mL, phosphorylated tau: 74.4 pg/mL, amyloidβ_1‐42: 163.6 pg/mL). Both patients presented with limited NFT pathology (Braak stage II). Therefore, normal total and phosphorylated tau levels may be characteristic of neuropathologically confirmed AGD and useful tools for differential diagnosis of Alzheimer's disease but not from PSP or DLB.

Regarding FDG‐PET findings, Adachi et al reported decreased uptake in the bilateral medial temporal lobes with laterality, sparing frontoparietal lesions in a pathologically confirmed case of AGD. ³ In the present case, the decreased uptake in the bilateral medial temporal lobe with right predominance was consistent with the case presented by Adachi et al. ³

The dysfunction of the nigrostriatal system is indicated by the decreased immunoreactivity of anti‐dopamine transporter immunostaining, as indicated by previous studies (Supplementary References S1, S2). Several studies have indicated the association between tau accumulations in the substantia nigra and Alzheimer's disease presenting with parkinsonism in the absence of neuronal loss or Lewy body pathology in the substantia nigra (Supplementary References S3, S4). A recent study implicated the association of aging‐related tau astrogliopathy in the substantia nigra with neuronal dysfunction and clinical manifestations, including parkinsonism (Supplementary References S5). Similarly, in this case, the tau immunoreactive structures, including AGs, pretangles, and granular fuzzy astrocytes in the substantia nigra, may be associated with parkinsonism in the absence of severe neuronal loss in the substantia nigra.

In conclusion, we report a case of AGD presenting with parkinsonism that was clinically diagnosed as PSP with progressive gait freezing. Neuropathological examination revealed an extension of the AGD pathology beyond the limbic system to the midbrain, as confirmed by both histopathological examination and biochemical analysis. Therefore, AGD should be included in the differential diagnosis of cases presenting with parkinsonism and cognitive impairment in the older population, in addition to PSP or DLB.

Author Roles

(1) Research project: A. Conception, B. Organization, C. Execution; (2) Statistical Analysis: A. Design, B. Execution, C. Review and Critique; (3) Manuscript: A. Writing of the first draft, B. Review and Critique.

R.S.: 1A, 1B, 1C, 3A, 3B

A.A.: 1A, 1B, 1C, 3A, 3B

T.M.: 1C, 3B

M.K.: 1C, 3B

A.M.T.: 1C, 3B

K.I.: 1C, 3B

K.K.: 1C, 3B

A.T.: 1C, 3B

M.H.: 1C, 3B

A.I.: 1C, 1B

S.M.: 1A,1B,1C, 3B

Y.S.: 1A, 1B, 1C, 3B

Disclosures

Ethical Compliance Statement: The authors confirm that approval from the institutional ethical committee was not required for this study. Informed consent was obtained from the patient's caregivers. We confirm that we have read the Journal's guidelines on issues involved in ethical publication and affirm that this work is consistent with these guidelines.

Funding Sources and Conflicts of Interest: This research was supported by grants from JSPS KAKENHI (numbers JP 22H04923(CoBiA) to YS and SM and JP22K15740 to TM), AMED (number JP21wm0425019 to YS and SM), and the Integrated Research Initiative for Living Well with Dementia (IRIDE) of the Tokyo Metropolitan Institute for Geriatrics and Gerontology (to YS and SM).

The authors declare that there are no conflicts of interest relevant to this work.

Financial Disclosures for the Previous 12 Months: The authors declare that there are no additional disclosures to report.

Supporting information

Data S1. Additional references for the discussion section.

Table S1. The distribution of argyrophilic grains and associated structures in the midbrain and basal ganglia.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.