Isolated Hypoglossal Nerve Palsy Associated with Internal Carotid Artery Dissection: A Systematic Review

Background: Isolated hypoglossal nerve palsy is a rare neurological condition with a broad differential diagnosis. Although neoplastic disorders are the most common cause, internal carotid artery dissection (ICAD) is an uncommon but clinically important and potentially reversible vascular etiology that is frequently underrecognized. This systematic review synthesized the available evidence regarding the clinical presentation, imaging findings, pathophysiological mechanisms, treatment, and outcomes of isolated hypoglossal nerve palsy associated with ICAD through a standardized patient-level descriptive analysis. Methods: This systematic review was conducted according to the PRISMA 2020 guidelines and prospectively registered in PROSPERO (CRD420261364863). PubMed, Scopus, Web of Science, and the Cochrane Library were searched from inception to April 2026. Manual reference screening and forward citation tracking were also performed. Studies reporting original, patient-level data on isolated hypoglossal nerve palsy associated with ICAD were eligible. Clinical, imaging, treatment, and outcome data were extracted and synthesized descriptively. In hybrid publications combining original case reporting with a narrative literature review, only eligible, original patient data were included in the quantitative synthesis, whereas the narrative review components were used for citation tracking and contextual comparison. Results: A total of 26 standalone primary publications were included, comprising 23 case reports and 3 case series. Two additional hybrid publications each contributed one eligible patient. One hybrid publication contained an original case-report component, whereas the other reported two original cases and was therefore considered to contain a case-series component, although only one of its patients fulfilled the eligibility criteria. Overall, the 28 publications contributed 32 eligible patients to the patient-level quantitative synthesis. The narrative review components of the two hybrid publications were used solely for citation tracking and contextual comparison. Patients were predominantly male (28/32, 87.5%), with a median age of 47 years. Tongue deviation (28/28, 100%) and tongue weakness (30/30, 100%) were the hallmark clinical features, followed by dysarthria (26/26, 100%) and dysphagia (18/22, 81.8%). All patients presented with isolated hypoglossal nerve palsy at presentation, without Horner syndrome or additional lower cranial nerve involvement. MRI was the most frequently reported imaging modality (29/32, 90.6%), whereas CTA was commonly used to characterize luminal abnormalities. Intramural hematoma (25/26, 96.2%), luminal stenosis (23/26, 88.5%), and external arterial enlargement (22/24, 91.7%) were the most consistent neuroradiological findings. Conservative medical management predominated (31/32, 96.9%). The available evidence was more consistent with a compressive mechanism related to subadventitial arterial wall expansion, although an ischaemic contribution involving the vasa nervorum could not be excluded. A favourable clinical outcome (complete recovery or marked improvement) was observed in 21/30 patients (70.0%). Overall, improvement of any degree, including partial recovery, was documented in 25/30 evaluable patients (83.3%). Outcome data should be interpreted cautiously because they derive predominantly from individual case reports. Conclusions: This systematic review provides an updated standardized synthesis of the available case-level evidence on isolated hypoglossal nerve palsy associated with ICAD. CTA and MRI/MRA provide complementary diagnostic information and may facilitate timely diagnosis when interpreted according to the clinical context. The available evidence identifies recurrent clinico-radiological patterns that may assist clinicians in recognizing this uncommon presentation while highlighting the need for prospective multicentre studies to better inform future diagnostic and therapeutic strategies.