Motor dysfunction in multiple-system atrophy (MSA), which is also referred to clinically as Parkinson’s plus syndrome, results from degenerative processes that affect several subcortical anatomic structures. Patients with different forms of MSA can present with symptoms that are very similar to those seen in PD. Differentiating these patients from PD patients can be very difficult particularly during the early stages. Clinically when a patient with parkinsonian symptoms fails to respond to L-DOPA therapy, MSA should be suspected as the pathological cause of motor dysfunction. Pathological changes may affect the striatum, cerebellum, brainstem, and the spinal cord nuclei. In a pattern of MSA referred to as striatonigral degeneration (SND) (Fig. 3.6.13), progressive atrophy and neuronal loss of the putamen and caudate as well as cell loss within the pars compacta of the substantia nigra without Lewy bodies are characteristic histologically. The patients with SND may also demonstrate seen in patients with PD. In contrast to PD, patients with SND may exhibit hypointensities in the putamen, which are thought to be due to increased iron deposition. The signal intensity of the putamen is dependent on the balance between hyperintensity from gliosis and hypointensity due to iron deposition. Olivopontocerebellar atrophy (OPCA) is another form of MSA in which degenerative changes involve the pontine nuclei and the transverse pontine fibers, middle cerebellar peduncles, inferior olives, and cerebellar cortex. Patients with OPCA have progressive ataxia and bulbar abnormalities. OPCA is typically seen in adults. There are familial as well as sporadic cases. The familial cases are commonly transmitted by autosomal dominant means. On MRI, atrophy of the transverse fibers of the pons, the cerebellum and the middle cerebellar peduncles may be detected (Fig. 3.6.14). A mild decrease in the width of the pars compacta may also be evident. Abnormal T2 hypointensity, seen in patients with SND, is not detected in patients with OPCA. In one form of MSA, there is neuronal loss involving the autonomic intermediolateral nuclei of the spinal cord. This condition is referred to as the Shy-Drager syndrome (SDS). In addition to symptoms of MSA, these patients also have symptoms of orthostatic hypotension, incontinence, and sexual dysfunction due to autonomic cell loss. On MRI, the findings in SDS reflect atrophic changes and abnormalities present in MSA.