Differential Diagnosis in Neurology

15.10. Written Language Impairments

Alexia without Agraphia 

These patients suffer an inability to comprehend written material. The patient can recognize words spelled aloud, graphesthetically produced words on the palm, or words constructed with blocks that are palpated. Most patients can recognize a few letters. Patients frequently suffer a partial or complete right homonymous hemianopsia and impaired naming and understanding of color names in the face of normal color vision. A few patients have impairment or loss of color vision, central achromatopsia. There may be an associated anomia. The usual lesion is occlusion of the left posterior cerebral artery with infarction of the left occipital lobe and the splenium of the corpus callosum which prevents transfer of visual information from the right occipital lobe to the left angular gyrus.

Occlusion of the dominant middle cerebral artery or its distal branches may also lead to an acquired loss of the ability to read or write from infarction of the parietal lobe. These patients often have concomitant mild hemiparesis, hemisensory loss, partial visual field deficit and anomic aphasia.

Lesions of the posterior inferior frontal cortex of the dominant hemisphere may impair the ability to comprehend syntactic structures and lack the ability to comprehend syntactic structures such as function words and endings. These patients may understand substantive words but cannot recognize relational words. This defect is seen in both spoken and written language. These patients also have difficulty in understanding sequences of semantically significant words. These patients frequently have a concomitant Broca's aphasia, hemiparesis and mild hemisensory loss.

Paralexia

Paralexia refers to substitutions of words or syllables when reading aloud. Synonym substitutions, somatic paralexia (truck for Lorrie) is associated with substitution of nouns for objects and an inability to read nonsense and function words. This type of dyslexia follows severe damage to the dominant hemisphere language areas and may be seen during recovery from complete alexia.

Agraphia

If patients suffer aphasia in spoken language, writing is also abnormal. Agraphia can be delineated into anterior frontal or posterior parietotemporal syndromes. The graphia associated with anterior Broca's aphasia is associated with large, poorly constructed words and is dominated by misspelling, and omission of function words and endings.

The agraphia of dominant posterior hemisphere lesions consists of well-formed words that generate abnormal sentences characterized by misspelling, abnormal word order and omissions that are devoid of meaning. Occasionally, posterior parieto-temporal lesion agraphia resembles that noted from anterior lesions.

Nondominant hemisphere lesions cause visual-spatial agraphia in which the patient is able to formulate correct letters and words but has great difficulty arranging them correctly on the page and having them progress from one line to the next. Isolated agraphia may occur from lesions of the angular gyrus of the dominant hemisphere or at times is associated with other aspects of Von Gerstmann syndrome. Aphasic agraphia has been recently described in a group of patients who were able t o write real words to dictation but not nonsense words. This phenomenon has been thought to be a disturbance of phoneme-grapheme transformation (surface agraphia) from a lesion of the posterior superior temporal lobe. The inverse of this deficit, an inability to write non-phonemic real words (e.g. through) with the ability to write phonetically nonsense words (geebe) has been ascribed to posterior inferior parietal damage and is thought to be a disorder of lexical grapheme transformation.

Anatomic Areas Associated with Agraphia

• Anterior-frontal (inferior frontal lobe and Broca's area)
• Posterior parietal temporal areas
• Acute confusional state
• Visual spatial agraphia (right parietal lobe)
• Gerstmann syndrome (BA 39, BA 40)
• Exner's area (BA 6 frontal lobe)
• Surface agraphia (posterior superior temporal gyrus)
• Dysgraphia (posterior inferior parietal lobe)

Word Finding Impairment

Inability to find specific words in spontaneous speech or in naming on confrontation is noted in all aphasias. Word finding impairment results from lesions in many different regions of the brain. It has been noted in many forms of dementia most prominently the FTD complex as well as with other pathologies such as increased intracranial pressure, acute confusional states, subcortical lesions and psychoses.

Word Production Anomia

• There are three categories of this type of aphasia:
  • Articular initiation difficulty
    • Articulatory initiation anomia is characterized by the aide that a phonetic or contextual clue gives to initiation of the correct word.
    • Articulatory initiation aphasia is seen in Broca's and transcortical motor aphasia while paraphasic anomia is concomitant with Wernicke's or conduction aphasia.
  • Paraphasic dysnomia
    • Paraphasic word production anomia is characterized by ease of initiation of a word that is contaminated with literal paraphasic substitutions.
    •  The incorrect word is often a neologism or an incorrect name.
  • Word elocution dysfunction.
    •  Word evocation anomia occurs in both anterior and posterior type of aphasia.

Word Selection Anomia

The patient is unable to name an object on confrontation by any sensory modality but can describe its use and can select it when it is named by the examiner. This pure word finding deficit is secondary to damage in Brodmann's area 37 (the temporooccipital junction of the dominant hemisphere).

Semantic Anomia

The patient is both unable to name the presented object and he can't select it when it is named. It appears as if the word has lost its symbolic meaning as both the comprehension and use of the name are deficient. Some patients may be able to repeat the required name even though they are unable to recognize the object or to name it themselves. This latter phenomenon is seen in both Wernicke's and transcortical sensory aphasia.

Disconnection Anomia

There are three different forms of disconnection anomia. Modality specific anomia naming is performed adequately in all sensory modalities except one. A patient with associative agnosia cannot name on confrontation but can easily do so by palpation. In auditory agnosia, the patient cannot identify the source of a sound but can name it when the object is seen. Category specific anomia refers to the inability of the patient to name a specific stimulus category although naming ability is preserved in all other spheres. A common example of this anomia occurs with color naming in posterior cerebral artery stroke. The patient may be unable to name presented colors or to select a color in response to its spoken name. The patient can match and correctly uses color names in purely auditory verbal tasks. Some patients may have greater difficulty in body part than object naming and some cannot name inanimate objects.

Aphasic Anomia

• Word production anomia:
  • Articulatory initiation anomia (Broca's aphasia)
  • Paraphasic anomia – Wernicke's arcuate fasciculus
  • Word evocation anomia:
    • Systemic disease
    • Anterior, posterior speech areas
    • Subcortical
• Word selection anomia (Brodmann's area 37)
• Semantic anomia (angular gyrus)
• Disconnection anomia:
  • Either or both hemispheres
  • Corpus callosum