Natural History of Speech and Swallowing Function in Neurofibromatosis 2 Includes Hypoglossal Dysfunction

Introduction: Neurofibromatosis Type 2 (NF2) patients report that speech and swallowing problems significantly affect their quality of life, but the etiology of these phenomena are poorly understood. Speech and swallowing deficits may arise due to the neuropathy of involved nerves, due to posterior fossa tumor growth, or as iatrogenic effects from neurosurgical procedures to remove these tumors.

Objective: To quantify speech and swallowing deficits, and their imaging correlates in NF2 patients.

Methods: One hundred and sixty-eight subjects were enrolled in a prospective, longitudinal study of NF2 between 2008 and 2013. Clinical and imaging evaluation was performed at each annual visit. The patients also completed a self-reported questionnaire that included responses regarding subjective speech and swallowing dysfunction. A formal speech-language pathology evaluation and modified barium swallow study (MBS, reported as ASHA Swallowing Independency Score from 1 through 7) was obtained when a speech/swallowing deficit was reported on the questionnaire. A hypoglossal canal abnormality on MRI was defined as abnormal nerve thickening or presence of tumor within or immediately adjacent to the hypoglossal canal.

Results: Of the 168 enrolled subjects, 55 (33%, median age = 31, females = 38) reported subjective speech and/or swallowing deficits. These patients underwent one (n = 37) or multiple (n = 18) MBS studies during 44.8 ± 10.4 month follow up. During MBS, a majority demonstrated near-normal swallowing (ASHA score >6, 82%), and no evidence of aspiration (aspiration/laryngeal penetration score =1, 96%). Prior to initial MBS consultation, 38 (69%) patients had undergone relevant neurosurgical procedures. In those with recent (< 1 week) posterior fossa surgery (n = 12), 2 (17%) patients had severe dysphagia and high aspiration risk on post-operative MBS. Both of these patients recovered to functionally independent swallowing status (without any evidence of aspiration) within 12 days after surgery (one patient recovered within 24 hours).

Unilateral (n = 10) or bilateral (n = 6) tongue deficits unrelated to previous history suggestive of hypoglossal nerve injury were detected on clinical exam. Unilateral hypoglossal canal abnormality (tumor or nerve thickening) on MRI with corresponding ipsilateral tongue deficit was seen in 11/16 patients (69%). Hypoglossal canal abnormalities were also detected in 14/39 (35%) subjects without tongue deficits, suggesting a more generalized incidence. Hypoglossal canal abnormality conferred a statistically significant increased risk of ipsilateral tongue deficit (RR=2.24, 95% CI=1.08 – 4.64). Univariate analysis revealed significant association between speech dysarthria score and hypoglossal canal tumor (p = 0.01) or hypoglossal thickening (p = 0.02).

Conclusions: MBS demonstrates near-normal function, even in patients that have undergone multiple neurosurgical procedures, despite subjective complaints of swallowing/speech difficulty. This pattern likely reflects adaptive mechanisms in speech/swallowing in response to inexorable tumor growth and cranial neuropathy. When post-operative dysphagia was observed, the deficit was transient and improved within days. Tongue deficits in NF2 appear to be unrelated to hypoglossal tumors or surgical injuries, and may be considered a component of natural history of NF2 as such. Patients with tongue deficits often have, hitherto undescribed, corresponding radiographic findings whose significance needs to be further explored.