In 1909, famous French psychiatrist Raoul Leroy experienced a bizarre mental phenomenon. Before him stood many figures, all colorful, friendly, and varying in appearances, but all sharing one characteristic – they were absolutely tiny. Leroy went on to outline these miniature characters in a paper, and dubbed them "lilliputian hallucinations", after the diminutive folk that inhabited Lilliput in Jonathan Swift's Gulliver’s Travels. 

Now, researcher Dr Jan Dirk Blom has explored this mental disorder in a systematic review of studies into lilliputian hallucinations, including how rare they are, how they are treated, and whether they pose a threat to those that suffer from them, published in Neuroscience and Biobehavioural Reviews.  

Those that suffer lilliputian hallucinations see an array of different characters, which roam the world in front of them and sometimes interact with the person. But this is no small gathering – these figures appeared in their thousands and, in some cases, even millions. Standing at an average height of just 23 centimeters (9 inches), these figures could be present for just a few seconds, or decades. 

“They involved tiny men, women, children, gnomes, imps, or dwarfs, often strikingly dressed as harlequins, clowns, dancers, soldiers, peasants, ‘mandarins’, ‘caftan wearers’, and so on. A recurring comment was that the figures were ‘rendered in exquisite detail’,” writes Professor Blom. 

In the review, Blom examined 145 case reports, which included 226 case descriptions, and looked for common themes between the presentations. Many of these case reports dated back decades, so reliability and how complete the records were varied greatly, but Blom worked with the available resources as faithfully as possible.  

Using numbers from historical studies, Blom estimated that around 30-80 clinical psychiatric patients per 10,000 will experience lilliputian hallucinations, making them markedly rare. However, these hallucinations were not as harmless as Leroy originally thought, with 18 percent of all the hallucinations becoming chronic and 8 percent of patients dying whilst experiencing them. It's likely the hallucinations didn’t directly cause these deaths, but the underlying causes of them may have significantly contributed. Alongside this, the review also disproved Leroy’s previous statements about the figures being friendly and affable, as the majority of hallucinations (46 percent of all cases) were associated with negative feelings, such as "frightening" or "annoying". 

To understand how these hallucinations occurred, Blom looked at correlations between their presentation and other psychiatric conditions. In 50 percent of cases, these miniature figures appeared when the patient had schizophrenia spectrum disorder, alcohol use disorder, or loss of vision, while the other 50 percent had a large array of other potential causes. It is likely they are directly caused by other neurological conditions, and Blom suggests treatment should be aimed at the prevailing issue and not the hallucinations themselves.