Histopathological investigation on six cases of pathologically confirmed MSA, using antibodies directed at a variety of α-synuclein epitopes, revealed substantial variation in α-synuclein protein deposition across both cases and brain regions within cases, providing evidence for strains of aggregated conformers that may differentially promote pathological prion-like spread.In 2020, researchers at The University of Texas Health Science Center at Houston concluded that protein misfolding cyclic amplification could be used to distinguish between two progressive neurodegenerative diseases, Parkinson’s disease and multiple system atrophy, being the first process to give an objective diagnosis of Multiple System Atrophy instead of just a differential diagnosis. Classification
MSA is one of several neurodegenerative diseases known as synucleinopathies: they have in common an abnormal accumulation of alpha-synuclein protein in various parts of the brain. Other synucleinopathies include Parkinsons disease, the Lewy body dementias, and other more rare conditions. Old terminology
Historically, many terms were used to refer to this disorder, based on the predominant systems presented. These terms were  discontinued by consensus in 1996 and replaced with MSA and its subtypes, but awareness of these older terms and their definitions is helpful to understanding the relevant literature prior to 1996. These include striatonigral degeneration (SND), olivopontocerebellar atrophy (OPCA), and Shy–Drager syndrome. A table describing the characteristics and modern names of these conditions follows:

Current terminology
The current terminology and diagnostic criteria for the disease were established at a 2007 conference of experts and set forth in a position paper.
The internal structure of the odontoid process is more compact than that of the body. The odontoid peg is the ascension of the atlas fused to the ascension of the axis. The peg has an articular facet at its front and forms part of a joint with the anterior arch of the atlas. It is a non-weight bearing joint. The alar ligaments, together with the apical ligaments, are attached from the sloping upper edge of the odontoid peg to the margins of the foramen magnum. The inner ligaments limit rotation of the head and are very strong. The weak apical ligament lies in front of the upper longitudinal bone of the cruciform ligament and joins the apex of the deltoid peg to the anterior margin of the foramen magnum. It is the fibrous remnant of the notochord. Other features
The pedicles are broad and strong, especially in the front, where they coalesce with the sides of the body and the root of the odontoid process. They are covered above by the superior articular surfaces. The laminae are thick and strong. They play a large role in the stability of the cervical spine alongside the laminae of C7.The vertebral foramen is large, but smaller than the atlas. The transverse processes are very small, and each ends in a single tubercle. Each process is perforated by the transverse foramen, which is directed obliquely upward and laterally. The superior articular surfaces are round, slightly convex, directed upward and laterally, and are supported on the body, pedicles, and transverse processes.