In 1909, French psychiatrist Raoul Leroy famously described his own hallucinatory experiences. The psychiatrist reported as many other patients had in previous years, seeing hallucinations that were… small.

The term ‘Lilliputian’ comes from the famous Gulliver’s Travels story, in which Gulliver arrives in the land of Lilliput, which is populated by tiny people. Leroy coined the term ‘Lilliputian hallucinations’ for seeing people, animals, or even objects that are greatly reduced in size.

Nowadays, this phenomenon is often described but little understood. In a study published in 2021, Jan Dirk Blom from Leiden University shed some light on this bizarre syndrome.

“Lilliputian hallucinations are not as harmless as traditionally assumed,” Blom starts out. Remarkably, despite their striking nature, he explains, they were never included in diagnostic classifications. Instead, they are typically considered benign hallucinations and even have the reputation of being enjoyable.

But when Blom dug a bit deeper, he found that the scientific literature includes quite a few cases with severe underlying pathology. Patients suffering from this type of hallucination would suffer from encephalitis, brain tumor, or even a stroke. Blom carried out a review of the existing scientific literature but found little information regarding the underlying source of these Lilliputian hallucinations.

Despite a relatively recent surge of interest, there doesn’t seem to be much new information about the condition. But Blom still came across some intriguing information.

Lilliputian hallucination can be very varied. They can feature tiny men, women, children, or even creatures such as gnomes, imps, or dwarfs. They’re often seen “in exquisite detail”, and often feature striking costumes, such as harlequins, clowns, dancers, or soldiers. In the vast majority of cases (83%), the hallucinations feature large groups of people, sometimes running into the thousands or even millions.

Because of the way these hallucinations manifest themselves, and because they almost always seem to be grounded in the surrounding environment (but rarely interacting with the patient), it seems that the cause is likely linked to the higher-level regions of perception. Whatever the cause or causes may be, they appear to fuse together sensory and hallucinatory content.

But it gets even weirder.

In about a quarter of the reported cases, tiny animals were seen (often in addition to human figures). Miniature tigers, cats, and hippopotamuses appeared in conjunction with other objects, such as bicycles, carriages, or musical instruments. The size of all people, animals, and objects fell within the 10-30 cm range, which is what Leroy first suggested when he described the condition.

Sometimes, the hallucinations go away on their own. The episodes seem to vary in length from a few seconds to several decades — with the notable case of a man who had lost his eyesight due to mustard-gas exposure during WWI. He constantly saw himself accompanied by tiny religious figures.

In fact, recovery was obtained in just 62% of the cases. In 18% of the cases, the hallucinations became chronic — and in 8%, whichever underlying condition caused these visions proved fatal due to the underlying conditions.

Lilliputian hallucinations are experienced by people of all ages and almost as often by men as by women, and while some patterns can be drawn, there’s a large variety reported in many of the cases.

“In spite of their reputation for being benign in nature, affability was reported in only 36 % of the cases and underlying causes were more often serious than not, with schizophrenia spectrum disorder, alcohol use disorder, and loss of vision accounting for 50 % of the cases. In the remaining 50 %, causes were extremely diverse, comprising neurological disorders such as stroke, brain tumor, encephalitis, and neurosyphilis, as well as systemic infectious diseases such as malaria and tuberculosis,” the study explains.

To add even more confusion, it’s likely that sometimes, cases go unreported or misreported, which means that these statistics may not be representative of all cases.

Blom suspects that understanding the failure behind size constancy may be key to understanding the underlying mechanism — and it’s this underlying mechanism that should be addressed with treatment.

However, without additional studies (especially imaging studies), we won’t get to the root of this bizarre condition that’s not nearly as benign as once thought.

“Neuroimaging studies, electrophysiological studies, treatment studies, and epidemiological surveys in larger patient samples are needed to allow for a better insight into lilliputian hallucinations and their underlying causes, including the role of size constancy,” the study concludes.