Abstract
Nonmotor symptoms are very common in neurodegenerative diseases. In patients suffering from amyotrophic lateral sclerosis (ALS), olfactory dysfunction was first reported more than 20 years ago; however, its pathophysiological correlates and further implications remain elusive. In this so far largest case-control study, we analyzed olfactory performance with the "Sniffin' Sticks," a validated olfactory testing kit used in clinical routine. This test kit was designed to investigate different qualities of olfaction including odor threshold, odor discrimination, and odor identification. ALS patients were mildly but significantly impaired in TDI score, the composite of the three subtests (ALS 27.7 ± 7.9, Controls 32.3 ± 5.8). In contrast to Parkinson's disease, ALS patients did not show impaired performance in the suprathreshold tests identification and discrimination. However, the odor threshold was markedly decreased (ALS 6.0 ± 3.4, Controls 8.77 ± 3.6). This pattern of olfactory loss resembles sinonasal diseases, where olfactory dysfunction results from impeded odorant transmission to the olfactory cleft. The evaluation of medical history and clinical data of ALS patients showed that patients with perception of dyspnea (TDI 25.7 ± 8.0) performed significantly worse in olfactory testing compared to those who did not (TDI 30.0 ± 7.4). In line with that, we found that in patients with preserved respiratory function (vital capacity >70% of index value), olfactory performance did not differ from healthy controls. These findings suggest that the mild impairment of olfaction in patients suffering from ALS should at least partly be considered as a consequence of impaired respiratory function, and odor threshold might be a marker of respiratory dysfunction in ALS.
Highlights
Amyotrophic lateral sclerosis (ALS) and its variants, primary lateral sclerosis and progressive muscular atrophy, are fatal neurodegenerative disorders with progressive degeneration of motor neurons and their axons [1,2,3]
Olfactory dysfunction is very common in neurodegenerative diseases, and in Parkinson’s disease (PD), hyposmia can precede motor symptoms for years
The significance of Nonmotor symptoms (NMS) in patients suffering from ALS and its variants is not fully elucidated yet, but scientific evidence is increasing [12]
Summary
Amyotrophic lateral sclerosis (ALS) and its variants, primary lateral sclerosis and progressive muscular atrophy, are fatal neurodegenerative disorders with progressive degeneration of motor neurons and their axons [1,2,3]. Disease spreading and involvement of other nonmotor regions in the brain seem to occur [4]. Corresponding nonmotor symptoms like gastrointestinal, autonomic, neuropsychiatric, and sleep disorders are well known in these diseases. Treatments of such nonmotor symptoms (NMSs) are fundamental elements in a modern and comprehensive health care for patients suffering from neurodegenerative diseases. Multiple other extramotor symptoms in ALS have been reported in the last years [11, 12], for example, autonomic dysfunction [13,14,15,16,17], sensory [18], and extrapyramidal symptoms [19, 20]. In patients suffering from amyotrophic lateral sclerosis (ALS), olfactory dysfunction was first reported more than 20 years ago; its pathophysiological correlates and further implications remain elusive
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