巴金森氏病是僅次於阿茲海默症最常見的神經退化性疾病。其致病機轉是由於環境因素和致病基因交互作用下，最終導致位在中腦黑質的突觸前多巴胺神經元的退化，造成紋狀體的多巴胺減少而產生運動障礙。在眾多致病基因中，LRRK2 基因上的突變與佔大多數的偶發型巴金森氏病最為相關。而病理的研究顯示，巴金森氏病患者在運動障礙症狀出現之前，會經歷漫長的運動前期。臨床上嗅覺低下發生在運動障礙之前，被認為是巴森氏症之危險因子。在這個時期，起始於腦幹的神經元退化早已緩慢的進展，最終會擴及至整個大腦。目前有許多的臨床工具包括嗅覺測驗、多巴胺系統核子影像，以及黑質穿顱超音波影像等，有助於了解巴金森氏病在運動前期特有的臨床標誌，能在運動障礙症狀出現之前診斷出腦部的退化，以利後續藥物或其他治療策略的介入。

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, which is caused by loss of dopaminergic neurons in the substantia nigra (SN) as a final result of interaction of environmental and genetic risk factors. Among various causative genes, mutations in the LRRK2 gene are most frequently associated with familial and sporadic PD. Pathological studies have shown neurodegeneration in extranigral systems, such as the olfactory bulb and vagus nucleus in brainstem, begins earlier than the nigrostriatal system and there is a long premotor phase in this relentlessly progressive disease. In the clinical aspects, hyposmia
antedates the motor symptoms and is considered as a risk factor of PD. Moreover, radiotracer imaging of the dopaminergic system detect dopaminergic neuronal loss antedating the appearance of motor symptoms.
Hyperechogenicity of SN shown by transcranial sonography has been related to a functional impairment of the nigrostriatal system and been proved to be a susceptibility marker for the development of nigral injury that can
be detected early in life prior to the onset of motor symptoms. These clinical tools effectively detect the premotor phase of PD, in which neuroprotective measures could possibly intervene.