This 3T MRI study shows that frontal cortical T2* hypointensity (likely reflecting iron accumulation/neuroinflammation) is ubiquitous in corticobasal syndrome, rarer in PSP, and its regional distribution correlates with specific motor and language deficits.

Provides a noninvasive imaging biomarker linking iron/inflammation topography to clinical phenotype in 4‑repeat tauopathies, aiding patient stratification, diagnostic accuracy, and mechanistic or therapeutic targeting of neuroinflammation/iron-related pathology.

BACKGROUND AND PURPOSE: Patients with corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP) often show the loss of the "swallow tail sign", which reflects degeneration of dopaminergic neurons and iron accumulation in the substantia nigra pars compacta, and peculiar neuroradiological signs which are, respectively, asymmetrical frontoparietal atrophy and midbrain atrophy. A T2* hypointense rim likely reflecting presence and distribution of neuroinflammation has been recently reported in the frontal cortex of CBS patients. Here we investigated (i) the frequency of conventional radiological signs associated with CBS and PSP and (ii) presence, distribution and frequency of the T2* signal hypointensity in the frontal cortex in CBS and PSP patients. In addition, (iii) we explored possible associations between T2* hypointensity in the frontal cortex and clinical symptoms. MATERIALS AND METHODS: Sixty-two patients were retrospectively included in the study (14 CBS and 48 PSP). Two neuroradiologists inspected the 3T MR datasets and recorded the presence/absence of: asymmetric frontoparietal atrophy, midbrain atrophy, loss of the "swallow tail sign" and T2* hypointensity of the frontal cortex. RESULTS: Asymmetrical frontoparietal atrophy and T2* hypointensity in the frontal cortex were more frequent in CBS patients (p<0.001) whereas midbrain atrophy and the loss of the "swallow tail sign" were so in PSP patients (p<0.001). The T2* signal hypointensity in the frontal cortex was detected in 14 CBS (100%) and five PSP (10%) patients and had three possible patterns of distribution associated with specific symptoms: (A) involvement of the hand knob only (three CBS and no PSP patients) in patients with unilateral ideomotor apraxia; (B) involvement of the primary motor cortex which extended beyond the hand knob (two CBS and five PSP patients); both CBS patients had bilateral ideomotor apraxia; (C) involvement of the primary motor cortex, the superior and/or the middle frontal gyrus (nine CBS and no PSP patients); all but one of these patients had ideomotor limb apraxia and all had speech/language impairment. CONCLUSIONS: The T2* signal hypointensity in the frontal cortex may be an additional radiological sign to be assessed in patients with atypical parkinsonism. Its distribution across the frontal gyri likely reflects clinical symptoms. The pathological assessment of CBS cases would support the robustness of these results.