Therapy-resistant symptoms in Parkinson's disease

In recent years, the management of Parkinson's disease (PD) has come a long way, leading to an increase in therapeutic options that now include oral and transdermal drug delivery, infusion as well as surgical treatments. Nonetheless, in the evolution of this complex neurodegenerative disorder, several symptoms remain refractory to dopaminergic therapy. It is our aim to review the literature to date and to bring them into focus, as well as emphasizing on pathophysiological mechanisms, profile of risk factors in their development, and therapeutic options. We will focus on freezing of gait, camptocormia, dysphagia and dysphonia, as well as cognitive impairment and dementia because they represent the far end of therapy-resistant symptoms, encompassing poor health-related quality of life and often a more reserved prognosis with either a rapid evolution of the disease, and/or merely a more severe clinical picture. Pathophysiological mechanisms and brain neurotransmitter abnormalities behind these symptoms seem to overlap to some extent, and a better understanding of these correlations is desirable. We believe that further research is paramount to expand our knowledge of the dopamine-resistant symptoms and, consequently, to develop specific therapeutic strategies.