Cutaneous α-Synuclein Signatures in Patients With Multiple System Atrophy and Parkinson Disease

Abstract

Background and objectives: Multiple system atrophy (MSA) is a progressive neurodegenerative disorder caused by the abnormal accumulation of α-synuclein in the nervous system. Clinical features include autonomic and motor dysfunction, which overlap with those of Parkinson disease (PD), particularly at early disease stages. There is an unmet need for accurate diagnostic and prognostic biomarkers for MSA and, specifically, a critical need to distinguish MSA from other synucleinopathies, particularly PD. The purpose of the study was to develop a unique cutaneous pathologic signature of phosphorylated α-synuclein that could distinguish patients with MSA from patients with PD and healthy controls.

Methods: We studied 31 patients with MSA and 54 patients with PD diagnosed according to current clinical consensus criteria. We also included 24 matched controls. All participants underwent neurologic examinations, autonomic testing, and skin biopsies at 3 locations. The density of intraepidermal, sudomotor, and pilomotor nerve fibers was measured. The deposition of phosphorylated α-synuclein was quantified. Results were compared with clinical rating assessments and autonomic function test results.

Results: Patients with PD had reduced nerve fiber densities compared with patients with MSA (p < 0.05, all fiber types). All patients with MSA and 51/54 with PD had evidence of phosphorylated α-synuclein in at least one skin biopsy. No phosphorylated α-synuclein was detected in controls. Patients with MSA had greater phosphorylated α-synuclein deposition (p < 0.0001) and more widespread peripheral distribution (p < 0.0001) than patients with PD. These results provided >90% sensitivity and specificity in distinguishing between the 2 disorders.

Discussion: α-synuclein is present in the peripheral autonomic nerves of patients with MSA and when combined with synuclein distribution accurately distinguishes MSA from PD.

Classification of evidence: This study provides Class II evidence that measurement of phosphorylated α-synuclein in skin biopsies can differentiate patients with MSA from those with PD.

Figure 1. Distribution of Phosphorylated α-Synuclein in Parkinson Disease (PD) and Multiple System Atrophy (MSA)

Biopsy locations are shown in the middle cartoon figure. Biopsies from a representative patient with MSA are shown in purple outlined boxes (A, B, C), and a patient with PD in green outlined boxes (D, E, F). The posterior cervical region biopsy of the patient with MSA, shown in panel A (A.a--A.f) reveals multiple α-synuclein positive regions in the sub-epidermal plexus. These positive regions are shown in expanded detail in A.a--A.c and A.d--A.f; phosphorylated α-synuclein in red (A.a and A.d), the overlying nerve fibers stained with PGP9.5 in green (A.b and A.e), and merged images in A.c and A.f). Similar images are seen in the proximal thigh (B) and distal thigh (C) biopsy sites. The biopsy from the posterior cervical region of a representative patient with PD, shown in panel D, reveals two adjacent positive fibers. The positive regions are shown in expanded detail in the yellow outlined box; phosphorylated α-synuclein in red in D.a, the overlying nerve fibers stained with PGP9.5 in green in D.b, and the merged image in D.c. A similar result is shown in the proximal thigh (E) with a single fiber containing phosphorylated α-synculein in E.a, the overlying nerve fibers stained with PGP 9.5 in green in E.b., and the merged image in E.c. The biopsy sites at the distal thigh (F) demonstrate regions where no phosphorylated α-synuclein is observed (F.a.), although nerve fibers stained with PGP9.5 are clearly identified (F.b.). White scale bar = 5 μm.

Figure 2. Topographical Distribution of P-SYN Across Study Subjects

The relative amount of synuclein deposition by biopsy site is shown for each individual subject; the larger the circle, the greater the synuclein deposition. The left panel is for subjects with MSA, and the right panel is for individuals with PD. When comparing the 2 panels, P-SYN deposition is greater and more evenly distributed than in MSA than in PD. DT = distal thigh; PC = posterior cervical; PT = proximal thigh.

Figure 3. Test Characteristics That Distinguish Multiple System Atrophy (MSA) From Parkinson Disease (PD)

The plots of phosphorylated α-synuclein are shown for patients with MSA (black circles) and PD (open circles). In Figure 1A, the plot of phosphorylated against the synuclein distribution coefficient is shown. In Figure 1B, the plot of phosphorylated against the intraepidermal nerve fiber density (IENFD) is shown. In both graphs, the cutoff thresholds identified using ROC curves are shown (see eTable 1, lww.com/WNL/C608). In Figure 1A, the upper left quadrant indicates patients with a high probability of MSA. In Figure 1B, the upper right quadrant indicates patients with a high probability of MSA. For both graphs, all other quadrants indicate patients with PD. In both graphs, a single patient with MSA and PD is misclassified.