Unilateral inferior olivary hypertrophy in a patient with primary progressive apraxia of speech

Hypertrophic olivary degeneration (HOD) is a rare neurological condition due to hypertrophy of the inferior olivary nucleus (ION), usually due to the disruption of the Guillain-Mollaret triangle (GMT). Here, we studied a patient with primary progressive apraxia of speech (PPAOS), a neurodegenerative disease condition of impaired motor speech production, who developed HOD and Parkinsonian features later in her disease course. We examined the patient’s disease course and evaluated various clinical, pathological, and neuroimaging variables. The patient developed motor speech problems at the onset and was diagnosed with PPAOS on her first visit. Over time, she developed features of an atypical Parkinsonian disorder, but she never developed palatal or dentatorubral tremors or ocular myoclonus. MRI scans were performed yearly at each visit according to the research protocol. During her sixth visit, changes in the left ION were first observed as hyperintensity on the T2-weighted MRI consistent with HOD. Using advanced neuroimaging techniques, we identified decreased fractional anisotropy (FA) and increased mean diffusivity (MD) in white matter tracts to and from the ION, supporting the diagnosis of HOD. A pathological diagnosis of progressive supranuclear palsy was rendered at autopsy. The findings from this case study demonstrate that ION degeneration and HOD can be a late feature of PPAOS, even in the absence of associated clinical signs and symptoms.