Involuntary inspiratory sigh in multiple system atrophy: A clinical and cerebral blood flow study

Involuntary inspiratory sigh (IIS) is a characteristic symptom of multiple system atrophy (MSA) and a supportive non-motor feature in the current diagnostic criteria. However, IIS during wakefulness has not been systematically investigated.

This study explored the clinical significance and neural correlates of IIS by comparing clinical characteristics and cerebral blood flow (CBF) single-photon emission computed tomography findings between patients with and without IIS, and evaluated a practical method for IIS assessment.

We retrospectively investigated 90 patients with clinically established or probable MSA. IIS was assessed via structured interview and direct examination. Patients were classified as IIS-positive if either method yielded positive results. Clinical characteristics were compared between IIS-positive and IIS-negative patients. Agreement between the two detection methods was examined. CBF was also compared between groups.

IIS was identified in 21 (23.3%) of 90 patients. The IIS-positive patients showed higher Unified Multiple System Atrophy Rating Scale Part I scores and REM Sleep Behavior Disorder Screening Questionnaire scores, and more frequent severe orthostatic hypotension in exploratory comparisons. Interview- and examination-based IIS assessments showed moderate agreement, and IIS was significantly more likely to be detected during interviews than during examinations. The IIS-positive patients exhibited reduced CBF in the bilateral supplementary motor area.

In MSA, IIS was associated with greater disease burden, more severe autonomic dysfunction, and reduced perfusion in the supplementary motor area. Interview-based assessment may help capture IIS in routine clinical practice. Clinicians should actively inquire about this clinically relevant symptom when evaluating patients with suspected MSA.