Agraphia

Agraphia describes an impairment or loss of a previous ability to write. Agraphia can occur in isolation, although it often occurs concurrently with other neurologic deficits such as alexia, apraxia, or hemispatial neglect. Clinically, agraphia can be divided into central agraphia (linguistic or aphasic agraphia) and peripheral agraphia (nonlinguistic or nonaphasic agraphia). To perform the act of writing, an individual produces a series of graphemes to communicate meaningful information. In the English language, graphemes consist of letters of the Latin alphabet. To write properly, one must first know the letters themselves and then understand how to organize letters to form proper words and grammatically correct sentences. Lesions disrupting these processes result in central agraphia. The individual must then know the set of coordinated movements to draw out letters correctly (praxis), the ability mentally to queue up the correct sequence of letters to make an entire word (motor programming), the visuospatial ability to guide a writing implement on a writing surface, and finally, the motor system to carry out these tasks. Impairment of these latter steps involved in the motor planning or motor action of writing leads to peripheral agraphia. Peripheral agraphia is characterized by difficulties in the physical act of writing, eg, forming letters and maintaining consistent letter shapes, sizes, and orientations. Patients with peripheral agraphia may exhibit errors like case substitutions, letter substitutions, and inconsistencies between print and cursive writing. Distinguishing between primary and secondary types of agraphia is essential. Primary agraphia refers to writing impairments caused by lesional insults directly to brain regions involved explicitly in writing. Primary agraphia is typically either an isolated or the predominant deficit in presentation; as such, it should not be attributable to other impairments, whether they be motor, linguistic, or cognitive. Secondary agraphia results from another primary disorder, whether visual (eg, hemianopia, visual agnosia), motor (eg, hemiparesis, tremor, dystonia), attentional (eg, hemispatial neglect), or cognitive dysfunction (eg, dementing diseases). The distinction between primary and secondary agraphia is clinically vital because treatment approaches differ significantly. Primary agraphia typically requires direct intervention targeting writing processes, whereas secondary agraphia is often addressed by first treating the underlying condition. The distinction also has neuroanatomical significance, as primary agraphia implicates specific writing-related neural circuits, whereas secondary agraphia reflects broader dysfunction across multiple systems. It must also be noted that the term aphasia is used inconsistently in literature. Aphasia most commonly refers to an acquired impairment of just spoken language, but it is also frequently used in clinical settings to encompass both written and spoken language impairments. This topic uses aphasia to refer to an isolated spoken language impairment. Peripheral agraphia can be viewed as analogous to dysarthria of written language in the sense that dysarthria denotes an impairment in the motor output of verbal language. Furthermore, in central agraphia, there can be a dissociation between written and spoken language ability; in some cases, there is even a difference in the type of aphasia manifested in the same patient, such as verbal nonfluent aphasia accompanied by written fluent aphasia. The qualifier term "linguistic" is used in this review to encompass written and spoken language issues. Agraphia is distinguished from illiteracy, in which the ability to write was never obtained. Dysgraphia typically denotes impaired handwriting as one part of a primary learning disability. It is also sometimes used to denote an incomplete acquired writing impairment and, in this case, is synonymous with agraphia. Paragraphia refers to a specific writing error analogous to paraphasic speech errors. The impairment of typing on a keyboard is known as dystypia (or dystextia in the case of mobile phone use) and often accompanies agraphia. Cases of isolated dystypia or dystextia suggest these may represent distinct impairments. Central agraphia arises from damage to the central neural processes involved in spelling and writing. Central agraphia impairs the linguistic components of writing, such as the ability to retrieve and manipulate graphemic representations, rather than the motoric execution of writing. Central agraphia manifests in numerous ways, including phonological agraphia, where patients struggle to write non-words, and lexical agraphia, where patients struggle to write irregular words. Central agraphia typically arises from lesions in the left hemisphere, especially the centers for language production in the frontal lobe, language comprehension in the temporal lobe, and connections between them running through the parietal lobe (eg, the arcuate fasciculus). Other areas, eg, parts of the motor cortex, auditory cortex, and visual cortex, also contribute to language processing.  Central agraphia can be further subdivided into phonological agraphia, lexical (surface) agraphia, deep agraphia, and semantic agraphia, reflecting the complexity of the neural processes involved in writing and underscoring the diverse neuroanatomical regions implicated by these disorders. occurs due to difficulty in impaired phoneme-to-grapheme conversion (sound-to-letter conversion), making it difficult to spell non-words or unfamiliar words. Patients can typically spell familiar words correctly but struggle with phonologically plausible errors when writing non-words based on their sounds. Persons with phonological agraphia typically remain able to spell familiar irregular words such as "subtle" but struggle when ambiguity between spelling and pronunciation obtains, such as between the words "steak" and "beak." Dyscravia is a disorder of phoneme-to-grapheme conversion in which written words are misspelled using proximate sounds, such as substituting a "t" for a "d." Dyscravia is classified as a subtype of phonological agraphia. causes difficulty spelling irregular words that do not obey standard phonetic rules and thus have atypical spellings (eg, "ghost" or "yacht"). As with phonological agraphia, regular words and non-words are usually spelled correctly. describes errors in the sequence and maintenance of letters within words, affecting both regular and irregular words. This condition is often due to a disruption in the short-term storage of graphemic representations. arises when writing becomes impaired due to a breakdown in semantic memory, disrupting the ability to access and use word meanings during the writing process. This condition often occurs secondary to a progressive loss of semantic knowledge, as can occur in patients with semantic dementia or the semantic variant of primary progressive aphasia (PPA). is a type of central agraphia where patients substitute words with semantically related ones (eg, writing "dog" instead of "cat"). This condition also involves phonological errors and difficulties with non-words, reflecting impairments in both the lexical-semantic and phonological types of writing. Despite its name, peripheral agraphia is a lesion of the central nervous system, not the peripheral nervous system. The main subtypes of  include: : This condition is haracterized by a disruption in the motor plans required for writing despite intact central spelling processes, patients with apraxic agraphia exhibit hesitant, incomplete, imprecise, or illegible handwriting. Lesions in the parietal and frontal regions, the thalamus, and the cerebellum most frequently account for presentations of apraxic agraphia. : This type of agraphia is characterized by difficulty in selecting and producing the correct letter shapes (allographs), in allographic agraphia, patients can spell words correctly but struggle with the visual form of letters, often substituting one letter form for another (eg, uppercase for lowercase). : This condition is characterized by disruptions in the short-term storage of graphemic representations, patients with this form of peripheral agraphia exhibit increased errors with longer words and have difficulty with both words and nonwords. is writing impairment due to errors of orientation to the writing instrument or surface. One common cause of visuospatial agraphia is hemispatial neglect, where one is unaware of half of the page—most frequently, this manifests with a blank left-hand side of a page. Other features suggesting visuospatial agraphia include errors of word spacing or word grouping and specific letter-writing errors such as incorrectly repeating strokes or even repeatedly writing the same letter multiple times. Letters or words may be superimposed. In these cases, writing errors are attributed to constructional apraxia. Note that constructional apraxia is a visuospatial disorder that does not refer to true apraxia (ie, an error of a skilled motor task) and is not to be confused with apraxic agraphia.