In July 2011, a woman presented at a psychiatric clinic in the Netherlands reporting something truly bizarre: for her entire life she'd seen multiple peoples' faces change into dragon-like faces - an hallucination that occurred many times a day.

"She could perceive and recognise actual faces, but after several minutes they turned black, grew long, pointy ears and a protruding snout, and displayed a reptiloid skin and huge eyes in bright yellow, green, blue, or red," the research team wrote in The Lancet in 2014. 

"She saw similar dragon-like faces drifting towards her many times a day from the walls, electrical sockets, or the computer screen, in both the presence and absence of face-like patterns, and at night she saw many dragon-like faces in the dark."

The 52-year-old was suffering from what's known as prosopometamorphopsia; a psychiatric disorder in which faces appear distorted.

The researchers couldn't work out what was causing this to occur. They performed a host of different brain scans including MRI, electroencephalogram (EEG), and neurological examinations, as well as blood tests. All were normal. 

"We see with the eyes but we see with the brain as well," well-known British neurologist Oliver Sacks says in a TED talk.

Sacks, who was part of the research team looking into the woman's case, has a face recognition disorder himself, where he doesn't process the shapes that make up a person's face as a face.

Researchers are unclear about what causes prosopometamorphopsia, but it can be induced by taking hallucinogenic drugs as well as strokes and tumours, which affect certain areas of the brain.

One such area is thought to be the fusiform gyrus, which is the part of our brain associated with face recognition. The fusiform gyrus is located in the ventral occipitotemporal cortex, and damage to it can make people hallucinate or unable to recognise faces.

Still, this woman's hallucinations were particularly rare, being so specific.

After much trial-and-error, her doctors found that an anti-dementia medication called rivastigmine conquered the dragons, for the most part.

Rivastigmine helps the human body synthesise the neurotransmitter, acetylcholine, which is involved with learning and memory. It's effective in helping early-onset Alzheimer's patients recognise their loved ones and helped this lady's face recognition too.

Before the treatment, the woman who saw dragons was unable to hold down a job, as her hallucinations interfered with her social interactions. 

Now, through the work of Sacks and his colleagues, she's had a steady job for the last three years and her colleagues say she's vastly improved.

The case study remains one of the most baffling and fascinating pieces of medical literature, and was published in The Lancet.