Wikipedia
Collagen disease
Collagen disease is a term previously used to describe systemic autoimmune diseases (e.g., rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis), but now is thought to be more appropriate for diseases associated with defects in collagen, which is a component of the connective tissue.
The term "collagen disease" was coined by Dr. Alvin F. Coburn in 1932, on his quest to discover streptococcal infection as the cause for rheumatic fever.
Usage examples of "collagen disease".
So far it's thought to be secondary to an undefined collagen disease.