Objectives Non-fluent primary progressive aphasias include progressive non-fluent aphasia (PNFA), a subtype of frontotemporal dementia,1 and logopenic progressive aphasia (LPA), an atypical form of Alzheimer’s disease.1–3 Progressive supranuclear palsy (PSP) overlaps with PNFA at both clinical and pathological levels; cognitive deficits are well recognised and may precede the typical motor syndrome.4 The hummingbird sign, reflected in a reduced midbrain to pons ratio, distinguishes PSP from other parkinsonian disorders. Our objective was to determine if the midbrain to pons ratio (M/P) could be used as a biomarker of PSP in patients with non-fluent primary progressive aphasia syndromes.
Methods Patients with PSP, PNFA and LPA were recruited. Patients were diagnosed clinically but pathological confirmation was available in a proportion of patients. Midbrain and pons areas were measured using Osirix Lite, a free DICOM viewer, and M/P was calculated.
Results Seventy-two participants were included (PSP 16, PNFA 18, LPA 16, and Control 22). PSP patients had motor features typical of the syndrome. M/P was significantly reduced in all disease groups, with greater reduction in PSP than in PNFA and LPA (p<0.001). An M/P ratio of less than or equal to 0.214 produced a positive predictive value of 92.9% for the diagnosis of PSP syndrome. Pathological confirmation revealed Alzheimer’s disease in 3 cases (all LPA), pathological PSP in 2 cases (1 clinical PSP and 1 PNFA) and corticobasal degeneration in 1 case (PNFA). M/P was 0.214 in the patient with clinical and pathological PSP, and 0.217 in the patient with PNFA due to PSP pathology.
Conclusions The M/P ratio was disproportionately reduced in PSP. Longitudinal studies are needed to examine the M/P ratio in patients with non-fluent aphasias in whom the PSP motor syndrome is yet to emerge. Larger studies of pathologically confirmed cases are also needed to establish M/P as a biomarker of PSP pathology.