A 44-year-old woman underwent 11C-Pittsburg compound B (11C-PiB), 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT), 99mTc-ethyl-cysteinate-dimer single photon emission computed tomography, and magnetic resonance imaging after presenting with progressive dementia, muscle weakness, and hypertonicity. Some of her family members had died of muscle weakness with early-onset dementia of unknown etiology. Neurological and psychological examinations revealed moderate dementia in general fields and muscle weakness in her upper limbs. 11C-PiB PET/CT revealed abnormal accumulations of amyloid in the bilateral occipital lobes, while physiological uptakes of 11C-PiB in areas that normally show high uptake, such as white matter, appeared relatively decreased. Meanwhile, cerebrospinal fluid (CSF) amyloid-β was decreased, and CSF total and phosphorylated tau proteins were increased. This case may be representative of a new category of amyloid deposition disease characterized by early-onset dementia, muscle weakness, and hypertonicity, or at least, a new uptake pattern of PiB in variant AD.