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BMJ   Visual command hallucinations in a patient with pure alexia
D H ffytche,
J M Lappin,
M Philpot
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Abstract
Around 25% of patients with visual hallucinations secondary to eye disease report hallucinations of text. The hallucinated text conveys little if any meaning, typically consisting of individual letters, words, or nonsense letter strings (orthographic hallucinations). A patient is described with textual visual hallucinations of a very different linguistic content following bilateral occipito-temporal infarcts. The hallucinations consisted of grammatically correct, meaningful written sentences or phrases, often in the second person and with a threatening and command-like nature (syntacto-semantic visual hallucinations). A detailed phenomenological interview and visual psychophysical testing were undertaken. The patient showed a classical ventral occipito-temporal syndrome with achromatopsia, prosopagnosia, and associative visual agnosia. Of particular significance was the presence of pure alexia. Illusions of colour induced by monochromatic gratings and a novel motion–direction illusion were also observed, both consistent with the residual capacities of the patient’s spared visual cortex. The content of orthographic visual hallucinations matches the known specialisations of an area in the left posterior fusiform gyrus—the visual word form area (VWFA)—suggesting the two are related. The VWFA is unlikely to be responsible for the syntacto-semantic hallucinations described here as the patient had a pure alexic syndrome, a known consequence of VWFA lesions. Syntacto-semantic visual hallucinations may represent a separate category of textual hallucinations related to the cortical network implicated in the auditory hallucinations of schizophrenia..................

The specialisation of the cortex for visual language also sheds light on a curious perceptual phenomenon encountered in a range of ophthalmological and neurological disorders—visual hallucinations of text. Visual hallucinations are common perceptual pathologies with estimates of between 11% and 57% of patients with visual pathway lesions, anywhere from the retina to the primary visual cortex being affected.5–7 The hallucinations fall into a restricted range of categories with about a quarter of patients with hallucinations related to eye disease experiencing text, isolated words, individual letters, numbers, or musical note hallucinations.8 The nature of such hallucinations is best conveyed by the reports of patients themselves. Typical descriptions include:

“....these hallucinations manifested themselves as very distinct lines of typed letters, in a random sequence, in my central vision... The phenomenon persisted for quite a period, during which time none of the letters ever made sense... I still get them from time to time but they appear extremely jumbled and at all angles...” (67 year old man, wet type macular degeneration).

“.....thin black letters in neat rows, sensible words often surrounded by masses of nonsense words....” (85 year old man, dry type macular degeneration).

“....writing on the ceiling which changes every time I look at it. Lists of words that do not make sense, an oval with inverted commas around it and inside the oval the letters AT. Labels with prices on them, eg ‘Super Something’ with one shilling or a pound sign and the size below.....” (76 year old man: glaucoma, bilateral retinal haemorrhages).

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Our patient was able to differentiate her visual hallucinations from visual imagery experiences. Her hallucinations had the vivid perceptual quality of real objects, were localised in external space, and were entirely outside her control. They would last several seconds and appeared on walls in front of her or to her left (her blind hemifield). When they first appeared, they could occur at any time but, by the time of her examination, they occurred predominantly in the evening. They consisted of warning messages or instructions in a scrawling hand written red script or black font print. Examples include:

“Don’t eat the fish.”

“Don’t take your tablets.”

“They’re after your money, we have got some of them but we are trying to find the others.”

“Throw the water at them to see if they are one of them.”

There was a conversational aspect to the messages, with questions, comments, and replies. She was able to read the hallucinated messages without having to scan each word. On one occasion she experienced hallucinations of figures consisting of ladies in bowling costume climbing over the television. She had not experienced other commonly reported hallucination categories such as phosphenes, grid patterns, or disembodied faces. Whatever their content, the hallucinations were always silent with no associated tactile or olfactory experiences.