Word-finding difficulty: a clinical analysis of the progressive aphasias

Abstract

The patient with word-finding difficulty presents a common and challenging clinical problem. The complaint of 'word-finding difficulty' covers a wide range of clinical phenomena and may signify any of a number of distinct pathophysiological processes. Although it occurs in a variety of clinical contexts, word-finding difficulty generally presents a diagnostic conundrum when it occurs as a leading or apparently isolated symptom, most often as the harbinger of degenerative disease: the progressive aphasias. Recent advances in the neurobiology of the focal, language-based dementias have transformed our understanding of these processes and the ways in which they breakdown in different diseases, but translation of this knowledge to the bedside is far from straightforward. Speech and language disturbances in the dementias present unique diagnostic and conceptual problems that are not fully captured by classical models derived from the study of vascular and other acute focal brain lesions. This has led to a reformulation of our understanding of how language is organized in the brain. In this review we seek to provide the clinical neurologist with a practical and theoretical bridge between the patient presenting with word-finding difficulty in the clinic and the evidence of the brain sciences. We delineate key illustrative speech and language syndromes in the degenerative dementias, compare these syndromes with the syndromes of acute brain damage, and indicate how the clinical syndromes relate to emerging neurolinguistic, neuroanatomical and neurobiological insights. We propose a conceptual framework for the analysis of word-finding difficulty, in order both better to define the patient's complaint and its differential diagnosis for the clinician and to identify unresolved issues as a stimulus to future work.

Fig. 1

An outline of clinical syndromes and underlying functional deficits in patients with word-finding difficulty. Relations between acute and chronic syndromes and primary and secondary functional deficits are shown. Numerals refer to the operational stages in the language output pathway (dotted lines indicate processes that are related to but not essential for language output): I, generation of a verbal message; II, sense of the verbal message; III, structure of the verbal message; IV, motor programming of speech. Key: esp, especially; HSV, Herpes simplex encephalitis.

Fig. 2

A clinical scheme for assessing the patient with word-finding difficulty, particularly in the context of degenerative disease. The scheme is organized as a ‘grid’ in which each column represents a key step in the clinical assessment, and each row represents a speech or language syndrome. Each entry in the grid represents an abnormality. Based on the initial assessment of features of the patient's spontaneous speech directed toward key language operations (left; see also Fig. 1), followed by key speech and language tasks (centre), the clinical speech or language syndrome is characterized. Identification of the clinical syndrome allows a differential diagnosis to be formulated, based on associated clinical features (right) including both cognitive and other neurological abnormalities. These associated features also allow primary and secondary effects on word-finding to be interpreted (Fig.1). See text for details. Key: filled circle: abnormal; AOS: apraxia of speech: *: as used in consensus criteria; †: nosological status not established; AD: Alzheimer's disease; bvFTLD: behavioural variant of frontotemporal lobar degeneration; CBD: corticobasal degeneration syndrome; CIRCUMLOC: empty, circumlocutory speech; COG: cognitive features; EPS: extrapyramidal syndrome; LTPS: lateral temporo-parietal syndrome; MND: motor neuron disease; PNFA: progressive nonfluent aphasia; PSP: progressive supranuclear palsy; SD: semantic dementia; SURFACE: surface (regularization) errors; VaD: vascular dementia.

Fig. 3

Structural anatomy of word-finding difficulty in degenerative disorders. Numerals and connecting arrows refer to the operational stages in the language output pathway (coded in Fig.1 and Table 2). Key anatomical areas are indicated. Arrows are bi-directional to indicate that flow of information between these areas is likely to be reciprocal. Brain magnetic resonance images illustrate some degenerative disorders with word-finding difficulty (the left hemisphere is on the right side in all coronal sections; TL, temporal lobe): (a) asymmetric (left greater than right) frontal lobe atrophy, dynamic aphasia; (b) focal left anterior/inferior temporal lobe atrophy, semantic dementia; (c) bilateral mesial temporal atrophy, Alzheimer's disease (anomia); (d) left posterior superior temporal/inferior parietal atrophy, progressive ‘mixed’, logopenic or jargon aphasia; (e) focal left superior temporal lobe/insular atrophy, progressive nonfluent aphasia; (f) focal left inferior frontal gyrus/frontal opercular atrophy, progressive apraxia of speech.

Fig. 4

Materials for assessing speech at the bedside. (Reproduced with permission of Professor EK Warrington.) (A) A beach scene, illustrating one means of eliciting conversational speech (see examples in Table 3). (B) A passage for reading aloud (see text).