The ubiquitin-binding protein p62 identifies argyrophilic grain pathology with greater sensitivity than conventional silver stains

The routine diagnosis of argyrophilic grain disease is fraught by the lack of availability of an easily applied reproducible stain that can highlight the grain pathology with sensitivity and with minimal background. The Gallyas silver iodide technique is not widely used and, even in experienced hands, is difficult to perform due to inconsistencies inherent in silver-based techniques on thin sections. Grain pathology can be detected using immunohistochemistry for phosphorylated tau protein, but the grain pathology is most often masked by background tau-positive material; leading to problems with interpretation, especially for practitioners seeing small numbers of cases. There is a need for a reliable immunohistochemical stain that can detect grain pathology and provide a clear contrast between grains and other tau-positive neurodegenerative pathologies. We have investigated the novel ubiquitin-binding protein p62 as a potential biomarker for grain pathology in argyrophilic grain disease. Four cases of argyrophilic grain disease, in which the pathology was determined using the Gallyas silver iodide technique, were re-assessed using paraffin-embedded sections immunostained with antibodies specific for p62. We found that the detection of grain pathology was more sensitive than with silver-based techniques and that the resolution of the pathology was significantly improved. We suggest that p62 could be used to replace the Gallyas technique in the routine diagnosis of argyrophilic grain disease.