The diagnosis of dystonia, an issue yet to be solved

Due to the lack of validated diagnostic biomarkers, the diagnosis of dystonia is based on clinical examination and therefore may be challenging and open to bias. The factors contributing to misdiagnosis of dystonia can be summarized in two main points: i) the huge variability in the clinical phenomenology of dystonia; ii) the existence of a bunch of medical conditions (i.e., pseudodystonia) mimicking the abnormal postures/movements induced by dystonia. This work is organized in two different part (Study 1 and Study 2) and the overall aim of the work is to help clinicians to better diagnosis idiopathic dystonia and functional dystonia. The objective of Study 1 is to identify clinical features suggestive of functional dystonia to guide physicians to distinguish functional dystonia from idiopathic dystonia. For this purpose, patient data were extracted from the Italian Registry of Functional Motor Disorders and the Italian Registry of Adult Dystonia. Patients with functional and idiopathic dystonia were followed up at the same clinical sites, and they were similar in age and sex. We identified 113 patients with functional dystonia and 125 with idiopathic dystonia. Sudden onset of dystonia, evidence of fixed dystonia, and acute peripheral trauma before dystonia onset were more frequent in the functional dystonia group. No study variable alone achieved satisfactory sensitivity and specificity, whereas a combination of variables yielded 85% sensitivity and 98% specificity. A diagnostic algorithm was developed to reduce the risk of misclassifying functional dystonia. The findings of Study 1 extend the current diagnostic approach to functional dystonia by showing that clinical information about symptom onset, fixed dystonia, and history of peripheral trauma may provide key clues in the diagnosis of functional dystonia. Study 2 was designed to provide practical guidance for clinicians in confirming or refuting suspected cervical dystonia, which is the most frequent type of dystonia. For this reason, participants of Study 2 were video-recorded according to a standardized protocol to assess 6 main clinical features possibly contributing to cervical dystonia diagnosis: presence of repetitive, patterned head/neck movements/postures inducing head/neck deviation from neutral position (item 1); sensory trick (item 2); and red flags related to conditions mimicking dystonia that should be absent in dystonia (items 3 to 6). Inter/intra-rater agreement among three independent raters was assessed by k statistics. To estimate sensitivity and specificity, the gold standard was cervical dystonia diagnosis reviewed at each site by independent senior neurologists. The validation sample included 43 idiopathic cervical dystonia patients and 21 control subjects. The best combination of sensitivity and specificity was observed considering all the items except for an item related to capability to voluntarily suppress spasms (sensitivity: 96.1%; specificity: 81%). The findings of Study 2 show that an accurate diagnosis of cervical dystonia can be achieved if, in addition to the core motor features, we also consider some clinical features related to dystonia mimics that should be absent in dystonia. In conclusion, this work sheds more light on the complex topic of the diagnosis of dystonia. Indeed, the algorithms proposed in Study 1 and Study 2 provide a helpful tool for clinicians in their practice.