Alice in Wonderland Syndrome and Charles Bonnet Syndrome: Similar but not so similar!

To the Editor

The letter by Trevizol et al. (2018) described a case of visual perceptual abnormalities secondary to neurological Varicella zoster virus (VZV) infection. Although the title termed it as Alice in Wonderland Syndrome (AIWS), the letter further went on to describe it as Charles Bonnet Syndrome (CBS). The terms AIWS and CBS appear to have been used synonymously in the letter, which are, on the contrary, unrelated and distinct syndromes. While both CBS and AIWS cause visual perceptual disturbances, CBS is classically characterized by complex, repetitive and stereotyped visual hallucinations and not visual illusions or distortions (Pang, 2016) whereas AIWS is a rare and complex neurological disorder characterized by distortions of visual perceptions, body schema and experience of time but without illusions, hallucinations or delusions.

Trevizol et al. (2018) appear to have described a patient who developed retrobulbar optic neuritis as part of neuromyelitis optica secondary to VZV infection. This involvement of the afferent visual pathway that caused partial visual impairment, and the subsequent development of Lilliputian visual hallucinations can be argued to be suggestive of CBS but not AIWS. Furthermore, unlike what is described in the letter, illusions are not marked by distortion of shape, size, motion or color but by false and new perceptions where the perceived object is an incorrect (not altered or distorted) recognition of a real object. Perceptual disturbances where the perceived object is correctly recognized but with a deviation from its customary appearance (like distortion of shape, size, motion or color) are called sensory distortions. Neither illusions nor visual distortions are characteristic of CBS whereas AIWS is characterized by visual distortions. Although dyschromatopsia can occur in AIWS, it is likely to have been directly related to optic neuritis in this patient. The absence of any other visual distortions, somesthetic or other non-visual distortions and the presence of visual hallucinations suggest that this was unlikely to be a case of AIWS.

Because AIWS is not characterized by psychotic symptoms, its consideration as a medical cause of psychosis by Galletly and Myles (2018) is inaccurate. Instead, it is more appropriately considered as a differential diagnosis of conditions that present with visual illusions and hallucinations. Although CBS is characterized by visual hallucinations, the absence of other hallucinations, delusions and formal thought disorder, as well as the usual presence of insight into the nature of symptoms, makes its consideration as a form of psychosis debatable.