Dystonia associated with parkinsonian syndromes is often manifested by dystonic postures (video segments 5 and 6) more than abnormal movements and they are rarely modified by a "geste
antagoniste." They include limb dystonia (from writer's cramp to a dystonic posture of the arm or foot), blepharospasm (and/or eyelid apraxia), orofacial dystonia, stridor, axial dystonia, and cervical dystonia. Axial dystonia is sometimes difficult to differentiate from rigidity, especially in the neck. In cervical dystonia, torticollis, retrocollis, or laterocollis are easy to define but antecollis can range from severe bent neck (considered to be a good clue for MSA) to abnormal neck flexion; in such cases, cervical dystonia can be found in up to 25% of MSA patients (17) and in most PSP patients (18).
As a rule of thumb, dystonia predominantly affects cranio-cervical musculature in MSA and PSP, although limb dystonia may be observed in PSP (leading to misdiagnosis of CBD). In fact, in CBD, the best predictors for the diagnosis are limb dystonia, ideomotor apraxia, myoclonus, asymmetric akinetic-rigid syndrome with late-onset gait or balance disturbances (19).
Levodopa-induced dyskinesias are observed in PD but are not infrequent in MSA. In MSA the presence of painful, dystonic, postural as well as orofacial and cervical dyskinesias are good clues for its diagnosis.
Myoclonus is sometimes difficult to differentiate from irregular tremor by clinical examination. Stimulus-sensitive myoclonus is elicited by either pinprick or light touch of the skin. It can be observed in MSA and in CBD patients. In PD patients, myoclonus is rare and may be related to levodopa (levodopa-induced myoclonus). Electrophysiologic testing helps to differentiate the stimulus-sensitive myoclonus in CBD with a pattern characteristic of cortical myoclonus (20) (video segments 5 and 6).
CONCLUSION: EXAMINATION AT A GLANCE
Very simple tests will help to get the most out of the clinical examination and medical history. This is particularly true for the bedside neuropsychological examination and eye movement exploration, which appear complicated but are not (video segments 3 and 4). Moreover, a refined and precise evaluation will increase the accuracy of the diagnostic criteria in clinico-pathological studies. For example, the precision of the information in the "clinical vignettes" is of great importance. This may allow clinicians to rename probable criteria into clinically definite or clinically probable. This high specificity of criteria is important for research studies, especially genetics or therapeutic studies.
As a rule of thumb, we suggest examining the patient "from head to feet" (see Fig. 1) in order to check all the diagnostic features included in the criteria for PD, MSA (video segment 7), PSP (video segments 1-4), CBD (video segments 5 and 6), and DLB.
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