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Corticobasal syndrome with Alzheimer's disease pathology

We read with great interest the article by Chand et al. entitled ‘‘Alzheimer’s disease presenting as corticobasal syndrome’’ in which a patient diagnosed clinically with corticobasal syndrome had pathology of Alzheimer’s disease (AD) at autopsy. Just recently, we have encountered a patient with the same clinical and pathological disparity. A 59-year-old, right handed woman presented with the right alien hand. Head MRI revealed mild generalized cerebral atrophy. SPECT study showed right temporal glucose hypometabolism. EEG demonstrated right temporal intermittent slowing. She was seen by us 2 years later complaining of some memory difficulties, right hand tremor, and general body bradykinesia. Her Mini-Mental State Exam (MMSE) score was 22 of 30. She had right hand rigidity and apraxia. Formal neuropsychological testing revealed evidence of a mild to moderate frontal subcortical dysfunction, characterized by marked bradyphrenia and visual processing deficits, as well as mild inattention and naming deficits. In contrast, the patient’s verbal memory functioning was normal for her age, with 100% retention of initially learned narrative information over a 30-min delay. Delayed free recall of a word list was mildly impaired, but improved to the normal range with cueing and recognition testing. MRI showed no significant change from previous study. She was placed on levodopa/carbidopa 25 of 100 three times a day with the recommendation of further upward titration of her dose if needed by her primary physician. When seen a year later, she was wheelchair bound and required assistance in all daily living activities. She reported that her right hand had ‘‘its own mind.’’ She had severe right hand rigidity and dystonia. Myoclonic jerks were seen. The MMSE was 13 of 30. Levodopa and donepezil provided no benefit. On examination performed 2 years later, there was severe right hand tremor, rigidity, and myoclonus with dystonic posturing. Frontal lobe release signs and gegenhalten were noted. A year later, she became mute. Rigidity and myoclonus became generalized. She lost a significant amount of weight because of dysphagia. She died 8 years after the disease onset and a brain autopsy was performed. Her brain weighed 800 g and had superior parietal lobule atrophy. There was normal pigmentation of substantia nigra and locus ceruleus. The neocortex had neuronal loss and diffuse gliosis, especially in superficial cortical layers, that was most marked in the frontal and parietal lobes. Many senile plaques (SP), neurofibrillary tangles (NFT), and neuropil threads were noted on thioflavin-S fluorescent microscopy. The hippocampus had only mild patchy neuronal loss with some NFT, Hirano bodies, and granulovacuolar degeneration. The entorhinal cortex had moderate to marked neuronal loss and NFT in layer II. The amygdala had many SP and NFT with atrophy, spongiosis, and gliosis. The Braak NFT stage was VI. The basal nucleus of Meynert and hypothalamus had NFT. There was SP in the striatum and globus pallidus. The thalamus and subthalamic nucleus were unremarkable. Substantia nigra had only mild focal neuronal loss and a few NFT. Immunohistochemistry for phospho-tau failed to reveal the dense thread pathology in gray and white matter in cortical and subcortical areas that is typical of corticobasal degeneration. No ballooned neurons were detected in the cortex. There were only a few thorn shaped astrocytes in basal structures, but no cortical astrocytic plaques. The final pathological diagnosis was AD, Braak stage IV, with relative hippocampal sparing. There are only a few reports of AD clinically presenting with the corticobasal syndrome. All 7 cases, including 6 reported in the literature and our patient (average age at death: 60 6 4 years; 4 men and 3 women), presented with typical clinical features and fulfilled the proposed research criteria of corticobasal syndrome. Pathologically, all cases had SP and NFT consistent with AD, but not corticobasal degeneration. Unlike the patient described by Chand et al., our patient did not demonstrate significantly impaired memory early in the course of illness. Although impairment was noted in other cognitive domains, the observed pattern (e.g., bradyphrenia, retrieval difficulties, and inattention) was more consistent with that of patients with subcortical disease. As suggested by Chand et al., the presenting clinical features of our patient suggest an atypical distribution of Alzheimer pathology early in the disease course, with unusual phenotypic expression. This clinical–pathological disparity is puzzling and requires further study of potential factors that may influence AD presentation.