Tauopathies are a class of neurodegenerative diseases characterized by the aggregation of abnormal tau protein.[1] Hyperphosphorylation of tau proteins causes them to dissociate from microtubules and form insoluble aggregates called neurofibrillary tangles.[2] Various neuropathologic phenotypes have been described based on the anatomical regions and cell types involved as well as the unique tau isoforms making up these deposits. The designation 'primary tauopathy' is assigned to disorders where the predominant feature is the deposition of tau protein. Alternatively, diseases exhibiting tau pathologies attributed to different and varied underlying causes are termed 'secondary tauopathies'. Some neuropathologic phenotypes involving tau protein is Alzheimer's disease, Pick disease, Progressive supranuclear palsy, and corticobasal degeneration.[1]

Reference
Wiki: Argyrophilic grain disease