Atypical presentations of Lhermitte's sign after treatment for human papillomavirus-associated oropharyngeal squamous cell carcinoma.

Lhermitte's sign (LS) is characterised by a brief electric shock-like sensation elicited by neck flexion that radiates down the spine and may extend into the posterior aspects of the legs. It is a clinical indicator of cervical or upper thoracic dorsal column dysfunction, most commonly due to demyelination or intrinsic spinal cord pathology. It may occur after head and neck (chemo)radiotherapy. We describe two patients with human papillomavirus-associated oropharyngeal squamous cell carcinoma who developed LS following chemoradiotherapy. One patient developed protracted LS lasting 20 months beyond completion of definitive concurrent chemoradiotherapy with volumetric modulated arc radiotherapy and weekly cisplatin and another patient developed protracted LS after adjuvant de-escalated volumetric modulated arc radiotherapy lasting 12 months beyond treatment completion. These cases show the variable course of LS in the modern conformal era and highlight its benign prognosis but potential for persistent symptoms that affect patient quality of life.