Recognizing Atypical Dopa-Responsive Dystonia and Its Mimics

Early Onset Parkinsonism: Differential diagnosis and what not to miss

Early Onset Parkinsonism (EOP) refers to parkinsonism occurring before the age of 50 years. The causes are diverse and include secondary and genetic causes. Secondary causes related to medications, inflammatory and infective disorders are mostly treatable and well recognized as they usually present with a relatively more rapid clinical course compared to idiopathic Parkinson's disease. Genetic causes of EOP are more challenging to diagnose especially as more of the non-PARK genes are recognized to present with typical and atypical parkinsonism. Some of the genetic disorders such as Spinocerebellar ataxia 2 (SCA2) and Spinocerebellar ataxia 3 (SCA3) may present with levodopa-responsive parkinsonism, indistinguishable from idiopathic Parkinson's disease. Additionally, some of the genetic disorders, including Wilson's disease and cerebrotendinous xanthomatosis (CTX), are potentially treatable and should not be missed. Due to the advent of next generating sequencing techniques, genetic analyses facilitate early identification and proper treatment of diverse causes of EOP. In this review, we outline the clinical approach of EOP highlighting the key clinical features of some of the non-PARK genetic causes of EOP and related investigations, which could assist in clinical diagnosis. This review also encompass genetic diagnostic approaches, emphasizing the significance of pretest counseling and the principles of bioinformatics analysis strategies.

Dystonia Diagnosis: Clinical Neurophysiology and Genetics

Dystonia diagnosis is based on clinical examination performed by a neurologist with expertise in movement disorders. Clues that indicate the diagnosis of a movement disorder such as dystonia are dystonic movements, dystonic postures, and three additional physical signs (mirror dystonia, overflow dystonia, and geste antagonists/sensory tricks). Despite advances in research, there is no diagnostic test with a high level of accuracy for the dystonia diagnosis. Clinical neurophysiology and genetics might support the clinician in the diagnostic process. Neurophysiology played a role in untangling dystonia pathophysiology, demonstrating characteristic reduction in inhibition of central motor circuits and alterations in the somatosensory system. The neurophysiologic measure with the greatest evidence in identifying patients affected by dystonia is the somatosensory temporal discrimination threshold (STDT). Other parameters need further confirmations and more solid evidence to be considered as support for the dystonia diagnosis. Genetic testing should be guided by characteristics such as age at onset, body distribution, associated features, and coexistence of other movement disorders (parkinsonism, myoclonus, and other hyperkinesia). The aim of the present review is to summarize the state of the art regarding dystonia diagnosis focusing on the role of neurophysiology and genetic testing.