Phonemic processing is below expectations and linked to word-finding difficulty in multiple sclerosis

Background: Word-finding difficulty is prevalent but poorly understood in persons with relapsing-remitting multiple sclerosis (RRMS). Objective: The objective was to investigate our hypothesis that phonological processing ability is below expectations and related to word-finding difficulty in patients with RRMS. Method: Data were analyzed from patients with RRMS (n = 50) on patient-reported word-finding difficulty (PR-WFD) and objective performance on Wechsler Individual Achievement Test, Fourth Edition (WIAT-4) Phonemic Proficiency (PP; analysis of phonemes within words), Word Reading (WR; proxy of premorbid literacy and verbal ability), and Sentence Repetition (SR; auditory processing of word-level information). Results: Performance (mean (95% confidence interval)) was reliably lower than normative expectations for PP (−0.41 (−0.69, −0.13)) but not for WR (0.02 (−0.21, 0.25)) or SR (0.08 (−0.15, 0.31). Within-subjects performance was worse on PP than on both WR (t(49) = 4.00, p < 0.001, d = 0.47) and SR (t(49) =3.76, p < 0.001, d = 0.54). Worse PR-WFD was specifically related to lower PP (F_2,47 = 6.24, p = 0.004, η² = 0.21); worse PP performance at PR-WFD Often (n = 13; −1.16 (−1.49, −0.83)) than Sometimes (n = 17; −0.14 (−0.68, 0.41)) or Rarely (n = 20; −0.16 (−0.58, 0.27). PR-WFD was unrelated to WR or SR (ps > 0.25). Conclusion: Phonological processing was below expectations and specifically linked to word-finding difficulty in RRMS. Findings are consistent with early disease-related cortical changes within the posterior superior temporal/supramarginal region. Results inform our developing model of multiple sclerosis-related word-finding difficulty.