Table 2.

Substantia nigra neuroimaging findings in Parkinson’s disease motor subtypes

Article	Patient numbers per subtype							Methods	Findings
	PD	TD	nTD	PIGD	AR	Mixed	HC
[44]	14						14	DTI	Reduced FA in PD patients SN was greater in the caudal region compared with the middle and rostral regions
[45]	12						20	DTI	Alterations of FA in the SN and putamen correlate with increased UPDRS motor scores
[46]	9	12					20	DTI	Reduced FA and increased MD and RD in the SN was largely driven by PIGD. Increased diffusivity in the globus pallidus correlated with disease stage and motor severity in PIGD
[48]		9		14			20	NM-MRI	PIGD have more severe signal attenuation in the medial SN of compared to TD, with the medial SN ipsilateral to the MAH having the greatest power to discriminate PD motor subtypes
[49]	70						20	MR	SN MR phase shifts are positively correlated with UPDRS-III and bradykinesia-rigidity subscores but not with tremor subscores
[50]		10			10		20	MR	Positive correlation between motor subtype ratio and R2* in the putamen, caudate, and thalamus but not in SN, with larger TD ratios having higher R2*

DTI diffusion tensor imaging, HC healthy control, Mixed mixed-ratio subtype, nTD non-tremor dominant, PD Parkinson’s disease, PIGD postural instability and gait difficulty, SN substantia nigra, TD tremor-dominant, MD mean diffusivity, RD radial diffusivity, MAH most affected hemisphere, MR magnetic resonance imaging, NM-MRI neuromelanin-sensitive magnetic resonance imaging, R2* relaxometry rate, FA fractional anisotropy, UPDRS Unified Parkinson’s Disease Rating Scale