LAUSR

We read with interest the excellent seminal study of Kaufmann et al demonstrating the natural history of pure autonomic failure (PAF). We offer the following comments. The authors found several distinguishing features predicting whether the major phenotypes associated with Lewy body disease (dementia with Lewy bodies and Parkinson disease) or multiple system atrophy (MSA) will eventually develop in patients with PAF, especially the presence or absence of hyposmia together with probable rapid eye movement sleep behavior disorder (RBD). Another factor indicating central nervous system (CNS) involvement not reported by Kaufmann et al is nocturnal stridor. Extensive clinical experience and previous evidence suggest that stridor, due to dysfunction of brainstem respiratory control neuronal systems, is found in MSA but not Lewy body disease. Timely recognition of stridor is crucial to enable treatment with continuous positive airway pressure or tracheostomy to prevent sudden death in patients with MSA. Future prospective assessment of nocturnal stridor in PAF cohorts is needed to confirm the value of stridor for distinguishing MSA from Lewy body disease, and to enable timely referral to sleep medicine specialists for potentially lifesaving treatments. We also suggest that the phraseology "phenoconversion to a manifest CNS synucleinopathy" may be misleading. If RBD is present, the patient already has definitive evidence that the CNS is involved in the disease process, as RBD originates from pontomedullary neuronal dysfunction. The results of the study indicate that in most if not all patients, PAF represents early manifestations of an evolving synucleinopathy. We suggest that this study should give impetus to rethinking current diagnostic criteria for MSA and Lewy body disease spectrum disorders, emphasizing the unitary nature of these conditions. Thus, a patient with autonomic failure, RBD, and objectively documented hyposmia should be considered to have probable Lewy body disease, even in the absence of parkinsonism or cognitive impairment. Similarly, a patient with autonomic failure, RBD, and stridor should be classified as probable MSA, even without extrapyramidal or cerebellar manifestations. Such an approach would align clinical diagnoses more accurately with the underlying pathology. Author Contributions All authors contributed equally to drafting this letter.