1 | INTRODUCTION AND BACKGROUND
Alzheimer’s disease (AD) is the most common neurodegenerative disease accompanied by dementia, which is considered due to the deposition of pathologic amyloid β and successive pathologic tau protein. The main clinical features of AD are an amnestic presentation, which includes learning impairment and problems recalling recently learned information, as well as nonamnestic impairments.1 Regional atrophy and hypoperfusion are typically observed in the medial temporal lobes, as shown by magnetic resonance (MR) imaging and [123I] iodoamphetamine single-photon emission computed tomography (IMP-SPECT), respectively. Mild cognitive impairment (MCI) is defined as the prodromal stage of dementia, with amnestic MCI considered that due to AD and supported by pathophysiological evidence.2
Sleep apnea syndrome (SAS) can cause cognitive impairment, which can be improved through continuous positive airway pressure (CPAP) treatment.3 Additionally, cancer in non-central nervous system malignancies can cause cancer-related cognitive impairment.4
We present a case of a right-handed 64-year-old Japanese man who visited our clinic with his wife, complaining of memory impairment. The patient was suspected of early-stage MCI due to AD based on IMP-SPECT findings. Pathologic amyloid β and tau protein deposition in the brain was also shown using 11C-Pittsburgh compound-B (PiB) positron emission tomography (PET) and 18F-THK5351 (THK5351)-PET, respectively.1 During the observation, the patient was diagnosed with SAS and treated successfully, although his cognitive impairment progressed. Eighteen months after the baseline visit, the patient might be diagnosed with early-stage AD. Nineteen months after the baseline visit, the patient was diagnosed with lung cancer without metastasis and underwent surgery. Several months after the surgery (2 years after the baseline visit), his cognitive ability as evaluated by neurocognitive testing showed significant improvement.
The cognitive impairment in our current case can therefore be considered to have been caused by carcinogenesis derived from the patient’s lung cancer. When diagnosing AD, it is important to collectively consider the patient’s physical illness rather than based solely on the results of neurocognitive tests and pathophysiological findings.