Non-fluent speech in frontotemporal lobar degeneration

Abstract

We investigated the cognitive and neural bases of impaired speech fluency, a central feature of primary progressive aphasia. Speech fluency was assessed in 35 patients with frontotemporal lobar degeneration (FTLD) who presented with progressive non-fluent aphasia (PNFA, n=11), semantic dementia (SemD, n=12), or a social and executive disorder without aphasia (SOC/EXEC, n=12). Fluency was quantified as the number of words per minute in an extended, semi-structured speech sample. This was related to language characteristics of the speech sample and to neuropsychological measures. PNFA patients were significantly less fluent than controls and other FTLD patients. Fluency correlated with grammatical expression but not with speech errors or executive difficulty. SemD and SOC/EXEC patients were also less fluent than controls. In SemD, fluency was associated with semantically limited content. In SOC/EXEC, fluency was associated with executive limitations. Voxel-based morphometry analyses of high-resolution MRI related fluency to gray matter volume in left inferior frontal, insula, and superior temporal regions for the entire cohort of FTLD patients. This region overlapped partially distinct atrophic areas in each FTLD subgroup. It thus appears to play a crucial role in speech fluency, which can be interrupted in different ways in different FTLD subgroups.

Why are patients with progressive nonfluent aphasia nonfluent?

“…5,6,11,25 This is the hallmark characteristic of this subgroup of PPA. We observed significantly nonfluent speech in a large, semi-structured sample in PNFA.…”

“…4,12,26 We examined small groups of patients, and our observations require confirmation with larger groups. Prior work with other patients with PPA has related semantic memory difficulty to nonfluent speech in semantic dementia, 5 but additional work is needed to examine factors contributing to nonfluent speech in the logopenic variant of PPA. With these caveats in mind, our observations suggest that grammatically mediated deficits constructing sentences during speech expression contribute to nonfluent speech in PNFA.…”

“…The hallmark feature of PNFA is reduced speech fluency. 5,6 In this study, we investigated 3 potential sources of nonfluent speech attributed to PNFA, including grammatic simplifications and errors, 1,5 a motorrelated disorder associated with speech-sound errors known as apraxia of speech (AOS), 3,7 and executive difficulty that limits mental search for words. 8,9 An executive deficit also is seen in patients with FTLD with a disorder of personality and executive functioning known as behavioral-variant frontotemporal dementia (bvFTD).…”

“…To investigate the basis for nonfluent speech in PNFA, a narrative speech sample and a neuropsychological evaluation were obtained. Since pilot work showed that description of a single complex picture does not provide a speech sample reflecting the participant's full breadth of language production capability, a large semi-structured speech sample was elicited 5,11 by asking participants to tell the story of the wordless children's picture book Frog, Where Are You? 18 At the beginning of a session, each participant looked through the book's 24 pictures.…”

“…The narratives were analyzed for speech fluency, quantified by words per minute (WPM); motor-related aspects of speech planning or AOS, quantified as % speech-sound errors per total number of words; and grammatic aspects of speech, measured by the % complex grammatic structures per utterance. These variables, described in previous publications, 5,11 are detailed in appendix e-1 on the Neurology ® Web site at www.neurology.org.…”