Agraphia is 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 (also called “linguistic” or “aphasic“ agraphia), and “peripheral” agraphia (also called “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 the letters of the Latin alphabet. To write properly, one must first have knowledge of the letters themselves, and then one must know how to organize letters to form proper words and grammatically correct sentences. Lesions disrupting these processes result in central agraphia. The individual must then have the knowledge of the set of coordinated movements to correctly draw out letters (praxis), the ability to “mentally queue up” a 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. Note that “peripheral” agraphia can localize to the central nervous system when it does not directly involve linguistic centers, such as in the case of motor agraphia due to a motor cortex lesion leading to the paresis of the writing limb.
There exist both clinical neurologic and neuropsychological classification schema to categorize the agraphias, and a clinical neurologic classification is used in this review. “Pure agraphia” is a term that is used to refer to an isolated impairment of writing without an associated relevant impairment in either language ability or praxis. While certain authors equate “pure agraphia” with apraxic agraphia, there is an effort by other authors to distinguish between “pure linguistic (or aphasic) agraphia” and “pure apraxic agraphia”. This review agrees with making this distinction on both a clinical and anatomic basis, and the evidence for supporting this distinction is discussed throughout this article.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 to encompass impairments of both written and spoken language.
This article uses the term “aphasia” to refer to an isolated impairment of spoken language. The peripheral agraphias can be viewed as analogous to “dysarthrias” of written language, in the sense that “dysarthria” denotes an impairment in the motor output of verbal language. Furthermore, in central agraphia, it is possible for there to 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 issues of both written and spoken language.
Agraphia is distinguished from illiteracy, in which case the ability to write is never obtained. The term “dysgraphia” is used most commonly to denote handwriting impairment as part of a primary learning disability, but 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, and they are analogous to the paraphasic errors of speech. The impairment of typing on a keyboard--dystypia, or dystextia in the case of mobile phone use--often accompanies agraphia, but cases of isolated dystypia or dystextia suggest these may represent distinct impairments.
Central (Linguistic) Agraphia
Agraphia with Nonfluent Aphasia
Agraphia, with nonfluent aphasia, typically reflects features of Broca’s aphasia, also referred to as nonfluent or motor aphasia. Letter and word output are lower than expected, with spelling errors due to letter omission. There may also be agrammatism marked by a paucity of prepositions and other grammatical elements, and calligraphy is poor. Dissociation may be present between written language and verbal language abilities, and written language may be inferior to verbal language.
Agraphia with Fluent Aphasia
Agraphia, with fluent aphasia, typically reflects the impairments in Wernicke’s aphasia, also referred to as fluent or sensory aphasia. Patients characteristically produce a normal quantity of words with normal calligraphy, but the content is nonsensical. There may be neologisms (“jargonagraphia”), as well as the nonsensical use or placement of proper words. Grammatical elements may be overused in relation to nouns. Written language ability may be superior to verbal language—sometimes markedly so.
Agraphia with Conduction Aphasia
Agraphia with conduction aphasia has been rarely described. The hallmark of conduction aphasia is a characteristic impairment of repetition known as the “conduit d’approche”: the patient will incorrectly repeat a word, but will sequentially iterate through phonologically proximate variations until the correct pronunciation is reached. Written analogs of the “conduit d’approche” have been described in patients with conduction aphasia.
Alexia with Agraphia
Alexia with agraphia simply refers to an impairment of both writing and reading ability, which can occur with or without aphasia. Patterns of written language impairment may follow those seen in the above categories.
Pure Linguistic Agraphia vs. Pure Apraxic Agraphia
An isolated impairment of writing that is not accompanied by any other language impairment or impairment in praxis can be considered “pure” agraphia. However, effort should be made to distinguish isolated agraphia due to a linguistic deficit from isolated agraphia due to writing apraxia.
Pure Linguistic Agraphia
Pure linguistic agraphia is present when an isolated impairment in written language occurs as a result of a disruption to central linguistic processes involved in writing. Verbal language and reading abilities are intact. There may be semantic and/or orthographic errors in writing. Calligraphy quality is often normal. Case-based evidence suggests that pure linguistic agraphia may be further subdivided into phonological and lexical subtypes. In phonological agraphia, there is an inability to spell pronounceable nonwords, and a retained ability to spell irregular words, which are exception words where spelling is dissociated from pronunciation--compare “steak” with “beak.” The reverse is found in lexical agraphia. Dyscravia is a more recently described disorder of phoneme-to-grapheme conversion in which written words are misspelled using proximate sounds, such as substituting a “t” for a “d”; dyscravia classifies as a subtype of phonological agraphia.
Pure Apraxic Agraphia
Pure apraxic agraphia is task-specific apraxia. As with pure linguistic agraphia, in pure apraxic agraphia, there is an isolated impairment in written language in the presence of intact verbal language and reading ability. However, the writing impairment here stems from disruption to processes involved in the motor output of writing, downstream of linguistic processes. As such, impaired calligraphy is often considered a hallmark of apraxic agraphia. There should be no other manifestation of ideomotor or ideational apraxia for apraxic agraphia to be considered “pure.” In some cases of pure apraxic agraphia, findings may be as subtle as a selective impairment in font, such as cursive script (“allographic agraphia”), or case (such as an isolated inability to write in upper-case).
Distinguishing between pure linguistic and pure apraxic agraphia
The distinction between pure linguistic apraxia and pure apraxic agraphia has been viewed as a significant diagnostic challenge. Certain techniques may help distinguish these two entities:
Calligraphy (writing quality): Calligraphy is often impaired in pure apraxic agraphia. As such, several authors have suggested that the presence of intact calligraphy points to pure linguistic agraphia. However, it remains unclear if one can have an isolated impairment of calligraphy involving linguistic processes affected in central agraphia with nonfluent aphasia.
Spelling: Oral spelling, which is considered a non-motor modality of “writing,” may be affected in linguistic agraphia, but intact in apraxic agraphia.
Copying: Writing that improves with copying written text may be useful in identifying pure linguistic agraphia, on the grounds that writing praxis is intact.
Non-motor writing: Besides oral spelling, other non-motor modalities to “write,” such as keyboard typing and mobile phone texting, may be preserved in pure apraxic agraphia and impaired in pure linguistic agraphia.
Pseudowords and irregular words: The writing of pseudowords and irregular words are used in the clinical neuropsychologic assessment of writing to localize disruptions in “phonological” and “lexical” processes, respectively. Such techniques may help identify pure linguistic agraphias if writing impairments are limited to these specific linguistic features.
Peripheral (Nonlinguistic or Nonaphasic) Agraphia
In apraxic agraphia, there is an impairment in the motor planning of writing. Apraxic agraphia can occur with or without other forms of apraxia; when isolated, it can be designated as pure apraxic agraphia. Apraxic agraphia is most commonly a form of ideomotor apraxia, in which case the individual has a desire to write but is unable to do so. However, ideational agraphia--in which the knowledge of the concept of writing itself is lost--has also been described.
Motor agraphia is broad and occurs due to the disruption of the motor system downstream of praxis, anywhere from the motor cortex to the peripheral nerve and muscle. Paretic agraphia is a result of paresis regardless of localization. Micrographia is hypokinetic motor agraphia most commonly associated with Parkinsonism and attributed to bradykinesia; it is marked by a progressive decrement of handwriting size. Hyperkinetic agraphia can result from a number of movement disorders such as tremor or chorea. Writer’s cramp is a task-specific focal dystonia of the forearm and hand muscles activated by writing. Writer’s cramp is considered simple when isolated to writing, and complex (or dystonic) when it carries over into other non-writing activities.
The reiterative agraphias include features such as perseveration, echographia (rewriting of phrases produced by the examiner), or paligraphia (rewriting of the same phrase produced by the patient).
Visuospatial agraphia is writing impairment due to errors of orientation to the writing instrument and/or writing 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, as well as 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 the term “constructional apraxia” is a visuospatial disorder and does not refer to true apraxia (i.e., an error of a skilled motor task), and is not to be confused with apraxic agraphia. Visuospatial agraphia can also be due to optic ataxia, in which there are errors of visual depth perception or oculomotor deficits.
Functional (Psychogenic) Agraphia
Functional agraphia can also occur as a manifestation of conversion syndrome. As with other functional neurologic disorders, framing functional agraphia within the model of traditional neuroanatomic localization can be challenging.
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