Klumke the cat: mysterious disease

Rescued cat in the Netherlands has mysterious disease: need information please!
Pictures available (warning: they are shocking). Click here for pictures

I’m asking on behalf of Corien, the person who rescued Klumke the cat, for information about this mysterious disease. Corien has lots of experience but has never in her life seen anything like this, and neither has her vet.

Problem:
bizarre amount of horny tissue forming in feet and ears.
I have pictures available – they are shocking.

You can see horny tissue coming out of the feet. This tissue partly covers the pads, curling around the nails, and growing beyond the nails. The “nails” were long about 10-15 cm (= 4-6 inches) curling around and touching the padding of the feet. Dirt from the litterbox got stuck in the curls and caused irritation almost inflammation.
The tissue of the ears was also horny.

What we know about Klumke:
male cat, about 1½ years old, present weight 2 kilograms = 4.4 pounds
We know that 1 year ago his weight was 5 kilo’s = 11 pounds.
At that time (6 months old)  he already showed the beginnings of this strange condition, and during the past year it grew out of control. He was rescued by Corien this past weekend.

Corien and the vet removed the horny tissue yesterday as shown on de last 3 pictures
She is looking for a solution how to prevent the horny tissue from forming again.
Has anyone seen this before or heard about this? If you know of someone who might know, could you please ask for us?

Klumke is being nursed back to health by Corien Tonnaer at Stichting Katimo in Roermond, The Netherlands