Adult polyglucosan body disease masquerading as "ALS with dementia of the Alzheimer type": an exceptional phenotype in a rare pathology.

We describe an exceptional clinical picture, namely, cognitive impairment of the Alzheimer disease type in a man who later developed manifestations typical of amyotrophic lateral sclerosis and who was subsequently found to have adult polyglucosan body disease (APGBD) upon postmortem neuropathologic explorations. The combined occurrence of amyotrophic lateral sclerosis and cognitive impairment of the Alzheimer disease type in APGBD has not been reported before. This case also underlines the diverse clinical presentation of this rare clinicopathologic entity (namely APGBD) and highlights the importance of recognizing the unusual association of clinical features in making the diagnosis.