Response to Letter to Editor: Mani, S., Golas, P., Rout, A., and Agarwal, R. Charles Bonnet Syndrome in Stevens–Johnson Syndrome: A Never Reported Phenomenon in Dermatology. Clinical Dermatology Review 2024; 8(2): 183-184

Dear Sir/Madam, I read with interest the letter to the editor by Mani et al. concerning the apparent emergence of Charles Bonnet syndrome (CBS) within a dermatological context.[1] The central premise of their study asserts that occlusion of the eyes was the precipitating factor for the onset of CBS. However, wider factors in this particular case may warrant further examination. Consider, for example, the following statement: “Our case fits the bill of CBS with visual hallucinations in the setting of preserved insight and intellect.” (p. 183) My concern with the above assertion is fourfold: First, the additional presence of auditory hallucinations is quite atypical for the syndrome. In fact, the CBS diagnostic criteria often report hallucinations occurring exclusively in the visual realm.[2–5] Second, the existence of secondary delusions of persecution is also not usually associated with CBS. If anything, such a clinical feature often precludes such a diagnosis.[2,6–8] This is because delusions of persecution are incongruous with preserved insight: an integral component of CBS. The authors themselves concede that until the intervention, the subject was displaying “psychotic symptoms,” which implies disturbed consciousness. Third, the authors correctly note that CBS can be elicited by eye patching and can resolve with its discontinuation.[9,10] Nonetheless, in this particular case, auditory hallucinations and secondary delusions were additionally present; either clinical feature is typically an exclusion criterion for CBS. The subject’s cluster of symptoms seems more akin to a form of delirium[11] than CBS. There could have been an acute psychic stress reaction to the emergence of Stevens–Johnson syndrome (SJS) symptoms, which was compounded by imposed sensory deprivation (i.e., bilateral eye patching). This combination could have contributed to the marked mental disturbances that subsequently ensued. The medical literature is replete with instances of delirious states emerging from sensory deprivation contexts.[12–14] In discussing “cataract delirium,” Weisman and Hackett stated, “the cataract is much less important than the masking since the condition may occur in any patient when bilateral bandages are employed.” (p. 1284) The same study[15] also asserted, “Delirium may be considered an adaptation of a vulnerable patient to severe psychic stress.” (p. 1285) Fourth, there are many potential medical explanations to account for the presence of visual hallucinations. As CBS is known as a diagnosis of exclusion, all other medical possibilities need to be first ruled out. One of these is an adverse reaction to a particular prescribed medication. In this instance, the elephant in the room may be the introduction of the anticonvulsant, carbamazepine (15 days before the emergence of diverse symptoms). Carbamazepine has been known for decades to precipitate severe side effects in some patients.[16] This includes psychosis,[17] auditory hallucinations,[18,19] visual hallucinations,[20–22] delusions of persecution,[23] and, most crucially, SJS.[24–28] It remains uncertain whether any or all of the subject’s symptoms could be attributable to carbamazepine toxicity, but a temporal association is plausible. In addition, a correlation has been noted between a specific genetic marker found in Indian patients and their susceptibility to carbamazepine-induced SJS.[29,30] Two final remarks regarding the downplaying of CBS in this case report. Tellingly, the authors reference Jayakrishnan Menon in their study.[31] His follow-up study, 2 years later, found an estimated CBS prevalence rate of 63% among the vision-impaired,[32] which stands in stark contrast to the authors’ claim that the condition is “rare” and “only a handful of cases reported to date.” (p. 183). Several studies have found an estimated prevalence rate of 30%–40% within this cohort.[33–35] While prevalence rates tend to be higher in Caucasian compared to Asian communities, in last year's Indian Journal of Psychiatry, four separate cases of CBS were reported in January alone.[36–39] Finally, the case report states of SJS: “Beyond their physical manifestations, these conditions inflict profound psychological distress on affected individuals.” (p. 183) The authors rightly acknowledge how debilitating SJS symptoms can be and yet curiously refer to CBS as ‘innocuous’ (p.184). Actually, Bonnet syndrome can be equally if not more distressing.[40–43] Some CBS content can be utterly terrifying to behold. Even so-called pleasant visual imagery can evoke most unpleasant thoughts. As visual hallucinations are renowned as a hallmark symptom of psychosis, many living with CBS are petrified that the mind is unravelling. That no subject volunteered their symptom in the aforementioned Menon study attests to how patients often dread disclosing, lest they be diverted to psychiatric services. CBS is not some benign medical curiosity, but rather a widespread phenomenon[44] that negatively affects one in three.[45] Routine, tactful screening for CBS among vision-impaired patients will help reduce unnecessary anxiety surrounding the condition. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.