Department of Otolaryngology-Head and Neck Surgery, New York-Presbyterian/Columbia University Irving Medical Center, New York, NY, USA.
Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA.
J Neurol. 2024 Mar;271(3):1170-1203. doi: 10.1007/s00415-023-12057-7. Epub 2024 Jan 13.
Strong evidence suggests that olfactory dysfunction (OD) can predict additional neurocognitive decline in neurodegenerative conditions such as Alzheimer's and Parkinson's diseases. However, research exploring olfaction and cognition in younger populations is limited. The aim of this review is to evaluate cognitive changes among non-elderly adults with non-COVID-19-related OD.
We performed a structured comprehensive literature search of PubMed, Ovid Embase, Web of Science, and Cochrane Library in developing this scoping review. The primary outcome of interest was the association between OD and cognitive functioning in adults less than 60 years of age.
We identified 2878 studies for title and abstract review, with 167 undergoing full text review, and 54 selected for data extraction. Of these, 34 studies reported on populations of individuals restricted to the ages of 18-60, whereas the remaining 20 studies included a more heterogeneous population with the majority of individuals in this target age range in addition to some above the age of 60. The etiologies for smell loss among the included studies were neuropsychiatric disorders (37%), idiopathic cause (25%), type 2 diabetes (7%), trauma (5%), infection (4%), intellectual disability (4%), and other (18%). Some studies reported numerous associations and at times mixed, resulting in a total number of associations greater than the included number of 54 studies. Overall, 21/54 studies demonstrated a positive association between olfaction and cognition, 7/54 demonstrated no association, 25/54 reported mixed results, and only 1/54 demonstrated a negative association.
Most studies demonstrate a positive correlation between OD and cognition, but the data are mixed with associations less robust in this young adult population compared to elderly adults. Despite the heterogeneity in study populations and outcomes, this scoping review serves as a starting point for further investigation on this topic. Notably, as many studies in this review involved disorders that may have confounding effects on both olfaction and cognition, future research should control for these confounders and incorporate non-elderly individuals with non-psychiatric causes of smell loss.
强有力的证据表明，嗅觉功能障碍（OD）可以预测阿尔茨海默病和帕金森病等神经退行性疾病的额外神经认知下降。然而，探索嗅觉和认知在年轻人群中的研究有限。本综述的目的是评估非 COVID-19 相关 OD 的非老年成年人的认知变化。
我们对 PubMed、Ovid Embase、Web of Science 和 Cochrane Library 进行了结构化的全面文献检索，以开展这项范围综述。主要研究结果是嗅觉功能障碍与 60 岁以下成年人认知功能之间的相关性。
我们对标题和摘要进行了 2878 项研究的评估，其中 167 项进行了全文评估，54 项选择进行数据提取。其中，34 项研究报告了年龄限制在 18-60 岁的人群，而其余 20 项研究包括了更混杂的人群，除了一些年龄超过 60 岁的人外，这个目标年龄段的大多数人也包括在其中。纳入研究中嗅觉丧失的病因包括神经精神障碍（37%）、特发性原因（25%）、2 型糖尿病（7%）、创伤（5%）、感染（4%）、智力障碍（4%）和其他（18%）。一些研究报告了许多关联，有时是混合的，导致关联的总数超过了纳入的 54 项研究的总数。总的来说，21/54 项研究表明嗅觉与认知之间存在正相关，7/54 项研究表明无关联，25/54 项研究报告结果混杂，仅有 1/54 项研究表明负相关。
大多数研究表明 OD 与认知之间存在正相关，但与老年人群相比，数据在年轻成年人中较为混杂。尽管研究人群和结果存在异质性，但本范围综述为进一步研究该主题提供了起点。值得注意的是，由于本综述中的许多研究涉及可能对嗅觉和认知都有混杂影响的疾病，因此未来的研究应该控制这些混杂因素，并纳入非老年且嗅觉丧失非精神性原因的个体。
