Pistol sign: unilateral hand dystonia predominantly associated with corticobasal syndrome

A 66-year-old right-handed woman with corticobasal syndrome (CBS) developed a distinctive unilateral hand dystonia, having previously presented with progressive cognitive and behavioural decline. An MR scan of the brain showed bifrontal cortical atrophy with subtle signal changes involving the left caudate nucleus and putamen. Electroencephalography and cerebrospinal fluid analyses were unremarkable. Over subsequent months, the patient developed worsening right-sided rigidity, limb apraxia, myoclonus and alien limb phenomena. During this progression, a characteristic abnormal hand posture became evident, comprising tonic flexion of digits III-V with extension of the thumb and index finger, resembling the configuration of a pistol. Retrospectively, we identified this 'pistol sign' in other patients, around 85% of whom fulfilled diagnostic criteria for CBS. This distinctive dystonic posture may serve as a useful bedside sign, contributing to earlier diagnosis and improved clinical management of patients with CBS.