Segmental Sudomotor Innervation in Harlequin Syndrome: A Case Report

Harlequin syndrome (HS) is a rare neurological disorder characterised by segmental anhidrosis and contralateral compensatory flushing, typically involving the face and extending to the neck. A 44‐year‐old man developed flushing of the right hemiface accompanied by left‐sided anhidrosis affecting the face, neck, upper chest and upper extremity 4 months after infection with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection. Although idiopathic anhidrosis associated with SARS‐CoV‐2 infection was initially suspected, imaging studies revealed a 43‐mm mass adjacent to the left T2–T3 intervertebral foramen. Progressive tumour enlargement paralleled worsening sudomotor dysfunction, leading to a diagnosis of symptomatic HS secondary to a presumed neurogenic tumour. Disruption of the sympathetic pathway at the T2–T3 level resulted in anhidrosis extending into the face beyond the corresponding sensory dermatomes. Magnetic resonance imaging and/or computed tomography are particularly useful for diagnostic evaluation of HS; however, the extent of imaging should be determined by the attending physician based on an understanding of the distribution of the sympathetic pathways.