Changes in the correlation between substantia nigra hyperechogenicity area and Parkinson’s disease severity at different Hoehn and Yahr stages

It is debatable whether the area of substantia nigra hyperechogenicity (SN+) in transcranial sonography (TCS) is related to Parkinson’s disease (PD) severity. Iron deposition, which is associated with the formation of SN+, may have different effects on dopamine nerve function as PD progresses. However, little research has explored the association between the SN + area and disease severity of PD in stages.

612 PD patients with sufficient bone window were retrospectively included from a PD database, and disease severity was assessed by the Unified Parkinson’s Disease Rating Scale (UPDRS) scores. Based on the Hoehn and Yahr (H-Y) scale, we classified the patients into seven groups (H-Y stage 1, 1.5, 2, 2.5, 3, 4, and 5) and then analyzed the correlations between the SN + area and the UPDRS scores separately.

Our results indicated a U-shaped relationship between the initial-SN + area and disease severity in PD: In the H-Y stage 1 group, the initial-SN + area was negatively correlated with the UPDRS total score (r = − 0.456, p < 0.001) and UPDRS-III score (r = − 0.497, p < 0.001). No correlation was observed in the groups of H-Y stages 1.5, 2, and 2.5. In the groups of H-Y stage ≥ 3, the initial-SN + area was positively correlated with the UPDRS total score and UPDRS-III score, with strongest correlation in the H-Y stage 5 group (all p values < 0.05). Moreover, the larger SN + area and average SN + area showed a similar evolutionary trend of correlation with UPDRS total score and UPDRS-III score.

Our study indicated a U-shaped correlation between the SN + area with the UPDRS total score and UPDRS-III score as H-Y stage progressed. The evolution of the correlation may reflect the evolution of underlying pathological mechanisms related to iron deposition in the substantia nigra.