Pointing index posture in progressive supranuclear palsy and corticobasal syndrome

Dear Sir, Focal dystonia is commonly associated with atypical parkinsonism. The topographical distribution of dystonia in these cases often serves as clinical indicators for the diagnosis of conditions such as blepharospasm and retrocollis in progressive supranuclear palsy (PSP), lower facial dystonia, antecollis, and Pisa syndrome in multiple system atrophy (MSA) and focal upper limb dystonia in corticobasal syndrome (CBS).[1] Barclay and Lang first described a specific dystonic hand posture (pointing gun sign) in PSP, characterized by an extension of the index finger and thumb.[2] However, thumb extension is inconsistent, and the pointing index posture is commonly observed along with the flexion of the other fingers [Figure 1]. In addition, the posture can be observed in CBS, with the cortical myoclonus of the same limb [Video 1]. The pointing index posture can even be observed in a 16th-century portrayal ("A Man") by Cornelis Anthonisz, probably depicting a patient with PSP.[3]Figure 1: Clinical images of patients with PSP [1A, 1B, 1D, 1E, 1G, 1I, and 1K] and CBS [1C, 1F, 1H, 1J, and 1L], showing an extension of the index finger with or without thumb extension, along with flexion of other fingers {"href":"Single Video Player","role":"media-player-id","content-type":"play-in-place","position":"float","orientation":"portrait","label":"Video 1","caption":"","object-id":[{"pub-id-type":"doi","id":""},{"pub-id-type":"other","content-type":"media-stream-id","id":"1_fvs1zm0h"},{"pub-id-type":"other","content-type":"media-source","id":"Kaltura"}]} A subtle form of the index finger pointing can be observed in other movement disorders such as cervical dystonia, essential tremor, and Parkinson's disease, where it is ill-sustained and typically seen only while walking.[4] However, the pointing index posture seen in PSP and CBS is considerably more obvious and persistent during rest or while performing any activity. Among the twelve patients being demonstrated, seven were diagnosed with PSP and five with CBS. Magnetic resonance imaging (MRI) scans of the brain showed dorsal midbrain atrophy in all seven patients with PSP, while asymmetric parietal lobe atrophy was observed in the five patients with CBS. FDG PET of the brain performed on three CBS patients revealed asymmetric parietal hypometabolism, particularly on the side contralateral to the pointing index posture [Figure 2]. Although there was no specific difference in the type of posturing between PSP and CBS patients, thumb extension, if present, was more commonly observed in PSP. The onset of this clinical sign varied widely, appearing between 9 months and 4.5 years after disease onset, with the majority of the cases developing within 2 years of disease onset.Figure 2: FDG PET brain image of a patient with CBS (1H), showing asymmetric parietal hypometabolism (Right > Left)The pathophysiology of focal hand dystonia in these disorders likely involves hyperexcitability of the cortex and brainstem due to loss of cortical and thalamic inhibitory interneurons, loss of inhibitory input from the somatosensory cortex, maladaptive plasticity, and disruption of the sensorimotor network beyond the basal ganglia.[1,5] In a patient with parkinsonism, the presence of a pointing index sign is an important clinical clue for suspecting tauopathies such as PSP and CBS, which should be confirmed with other clinical findings. Acknowledgment We acknowledge the caregivers of these patients for their constant support. Author contribution Research project: JG Conception: JG Organization: JG, SM, NS Statistical analysis: Execution: JG, SM, NS Manuscript preparation: Writing of the first draft: JG Review and Critique: HK Ethical compliance statement The authors confirm that the approval of an institutional review board/ patient consent was not required for this work. We also confirm that the patients have given written informed consent for the publication of his video. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.