Personalized medicine is an emerging field that seeks to tailor the treatment of individual patients based on their clinical characteristics, biomarkers, genetics, and other factors
[1][2]. Other factors include specific comorbidities, complications, and patient background. To date, personalized medicine in Parkinson’s disease (PD) has not been fully realized due to barriers such as cost and genetic counseling although personalized medicine is used in PD patients in clinical settings when treatments are tailored based on motor and non-motor features
[3][4][5][6][7].
PD is a heterogeneous disorder in which motor and non-motor features of varying types and degrees may appear quite separately in individuals
[1][8]. Indeed, the etiology and pathogenesis of PD include a mixture of factors without any diagnostically reliable biomarkers; therefore, the diagnosis of PD is still based on a clinical assessment
[9][10]. It is known that the prognosis of PD differs between clinical types, with tremor-dominant types progressing slower than postural instability gait difficulty (PIGD) types
[11]. The Parkinson’s Progression Markers Initiative (PPMI) clinical study has revealed more detailed subtypes of PD
[12]. The authors classified PD into mild motor-predominant, intermediate, and diffuse malignant types
[12]. Several studies have been undertaken to address and detect possible biomarkers, which may predict the progression of individual PD patients
[13].
Historically, the first PD treatments involved a surgical approach. In 1952, Narabayashi et al. performed the world’s first pallidotomy for PD patients and described its positive effect
[14]. In the early 1960s, L-dopa therapy was initiated, but initially, low doses failed to show efficacy in many PD patients; Cotzias then initiated the use of high-dose therapy, and the modern regimen for L-dopa therapy was established
[15]. L-dopa is still the gold standard, and its combination with dopamine agonist, monoamine oxidase type B inhibitor, catechol-O-methyltransferase inhibitor and/or non-dopaminergic medication has been used to treat L-dopa related motor and non-motor complications for many years. However, in the advanced stage, despite adjustments to these medications, it is impossible to manage these complications, and finally surgical intervention is required in some patients. The use of stereotactic neurosurgery declined with the introduction of the drug L-dopa as an effective oral medication; but stereotactic neurosurgery was revived when it was shown to be effective in treating motor complications including wearing-off and dyskinesia
[16][17]. Later, deep brain stimulation (DBS) was introduced, and became the gold standard of treatment for advanced PD motor features
[18]. Today, various advanced treatments such as DBS, radiofrequency, MR–guided focused ultrasound (MRgFUS), gamma knife, levodopa-carbidopa intestinal gel (LCIG), and apomorphine are available, although the availability of treatments varies depending on country and region. Clinical practice guidelines for early treatment of PD have been published in various countries and are often recommended by experts
[19][20][21]. Standard pharmacological and non-pharmacological treatments are required during treatment, and the need for personalized medicine becomes more obvious when aiming to achieve an appropriate symptomatic and disease-modifying treatment with the right dose, right time, and minimum side effects in a specific patient. On the other hand, guidelines for the treatment of advanced PD have not been established, and in particular, the indication criteria and exclusion criteria for device-aided therapy have not been clarified. DBS and LCIG are the most established treatments for advanced stage PD in recent years, apomorphine subcutaneous infusion and MRgFUS have also become available, and efforts to incorporate them into personalized medicine will become important in the future. This review focuses on the advanced treatment of PD including cell therapy and gene therapy. Furthermore, we discuss aspects of personalized medicine that are currently available for the advanced treatment of PD.