I often write about rare medical disorders, but there is one extraordinary case which is so strange, that there is only one documented instance of it in medical history.

It involves a man who was both a dwarf as well as a giant over the course of his lifetime.

Adam Rainer was born in Graz, Austria to average-sized parents in 1899.

When WW1 broke out, Rainer tried to enlist in the army, but at 4'6.3'' inches tall, he was deemed too short and weak. A year later, Rainer tried again, and although he had grown a full 2 inches, the army rejected him once more on the basis of his height.

Standing 4'8.3'' inches tall at the age of 19, Rainer was considered a dwarf, being nearly 2 inches below the cut-off (4'10'').

Although he was short, medical reports from the period state that Rainer had abnormally large hands and feet for his height.

When he first tried to enlist in the army, he wore shoes sized US 10 (EU 43).

Three years later, his feet had doubled to a size US 20 (EU 53), though his height remained relatively static. To put this in perspective: US basketball player, Shaquille O'Neal, wears shoes sized US 23.

At the age of 21, all this changed.

Rainer is pictured on the left next to a man of average height. The Tallest Man Rainer (pictured right) suddenly began growing at an alarming pace.

Over the next decade, he grew from just under 4'10'' to a shocking 7'1''. During this period, Rainer also began developing a severe spinal curvature.

What exactly was the cause behind this growth spurt?

Between 1930 and 1931, Rainer was examined by Drs A. Mandl and F. Windholz, during which time they discovered he was suffering from a condition known as acromegaly.

In Rainer's case, this was caused by a tumour on his pituitary gland which led to an overproduction of growth hormones in his body. This was the reason behind his strange appearance, for Rainer didn't just have abnormally large hands and feet. He also had a protruding forehead and jaw, as well as thick lips set over widely-spaced teeth.

Below are images of man with acromegaly – you can see the effects of this syndrome on his facial features as he ages:

The two doctors decided to operate despite believing the chances for success were small given the fact that the tumour had been growing for over a decade. A few months after surgery, Rainer was measured again. His standing height had remained the same, though his spinal curvature was more severe, indicating that he was still growing, albeit at a much slower rate.

Rainer's health continued to deteriorate. He went blind in his right eye, and began suffering hearing loss in his left ear. Over time, his spinal deformity became so pronounced, Rainer was confined to bed.

He died, aged 51, measuring 7'8'' – though some newspapers reported his height as 7'10". He is the only man in history to be classified as both a dwarf as well a giant; and for me, he is a testament to the marvels of the human body.