Background/Objectives: Imaging of both cardiac sympathetic denervation and nigrostriatal dopaminergic degeneration can support the diagnosis of Parkinson's disease (PD). However, their temporal relationship and combined diagnostic value remain unclear. This review addresses (1) whether nigrostriatal degeneration and cardiac sympathetic denervation are correlated in PD and (2) the comparative and combined diagnostic accuracy of striatal dopaminergic and cardiac sympathetic imaging in PD. Methods: We searched PubMed (October 2025) for studies assessing both a striatal dopaminergic and a cardiac sympathetic imaging biomarker in the same PD cohort, supplemented by citation chaining. Diagnostic accuracy studies were evaluated using QUADAS-2. Results: Nineteen studies met the inclusion criteria. Ten studies examined within-subject associations; six reported significant correlations ranging from weak to strong (ρ ~0.2-0.8). Two studies observed a significant correlation for the akinetic-rigid subtype but not for the tremor-dominant subtype of PD. Ten studies compared diagnostic accuracies, five of which used pre-defined thresholds and consistently found higher sensitivity for [123I]FP-CIT SPECT (78-100%) compared to [123I]MIBG scintigraphy (65-82%), but higher specificity for [123I]MIBG (range 75-100%) than for [123I]FP-CIT (range 11-73%). Adding [123I]MIBG scintigraphy to [123I]FP-CIT SPECT generally increased specificity but had inconsistent effects on overall accuracy. QUADAS-2 revealed substantial risks of patient selection bias, data-driven thresholds, and limited blinding. Conclusions: Reported correlations between nigrostriatal dopaminergic degeneration and cardiac sympathetic denervation in PD are inconsistent, likely reflecting both methodological heterogeneity and real variation between phenotypes. There may be a stronger correlation in the akinetic-rigid phenotype. Dopaminergic imaging is more sensitive in early PD, while cardiac sympathetic imaging is more specific for differentiating PD from atypical Parkinsonian syndromes. However, study designs greatly restrict the generalizability of reported diagnostic accuracies.