Morphology of Rosacea

What is the morphology of rosacea? Morphology in biology deals with the outward appearance (shape, structure, colour, pattern) as well as the form and structure as opposed to physiology which deals with the function of an organism.

Why bring up the morphology of rosacea? It has to do with the recent classification of rosacea into four subtypes and one variant by the NRS 'expert' committee in helping to diagnose rosacea so that everyone can be on the same page when discussing rosacea. While this classification has proved helpful, it is of note to read you a line from the official report of this expert committee:

"As knowledge increases, it is hoped that the definition of rosacea may ultimately be based on causality, rather than on morphology alone."

What we have is basically the first time a group of physicians got together to try to standardize what rosacea is and what it is not by a group of 'experts' on rosacea. However the committee concluded with this statement:

"This investigational instrument is intended to set the stage for a better understanding of rosacea and its subtypes among researchers and practitioners by fostering communication and facilitating the development of a research-based classification system. As a provisional standard classification system, it is likely to require modification in the future as the pathogenesis and subtypes of rosacea become clearer, and as its relevance and applicability are tested by investigators and clinicians. The committee welcomes reports on the usefulness and limitations of these criteria."

So you could say that this is a good start and may prove to continue to be the standard until proven otherwise or it is quite possible that as more knowledge is gained this classification system may be revised. What is important to understand is that the entire classification system is based on morphology rather than physiology, or what the 'expert' committee terms 'causality' or what causes rosacea. Since the jury is still out on what exactly is causing rosacea and the fact that rosacea's definition is still controversial amongst the medical community, we need to keep an open mind about what constitutes rosacea.

What I find puzzling is that the 'expert' committee excluded three rosacea mimics as not variants of rosacea:

Rosacea fulminans, Steroid-induced acneiform eruption, and Perioral dermatitis

The committee has their reasons for this and said:

"The committee noted that certain disorders may have been prematurely identified as associated with rosacea or as a variant of rosacea, and for clarity should be recognized at this time as separate entities. There is insufficient basis at present to include the following conditions as types of rosacea." So it is possible that in the future these three could be rosacea variants. What is puzzling to me is absolutely no mention of demodectic rosacea.

So if in the future we learn that rosacea is caused by a single entity or by several different entities or in combination we might have a completely different classification system or one similar but based upon 'causality' rather than morphology. And most important is that we certainly need more knowledge about rosacea. It remains truly a mystery and while the work of the NRS 'expert' committee is noteworthy we certainly need more information.

More info:

Classification of Rosacea Remains Controversial

Diagnosing Rosacea

Is Rosacea a ‘Complicated Diagnosis Path’ and Mysterious Disorder?

Cause of Rosacea Revisited

Sources

Standard classification of rosacea:
Report of the National Rosacea Society Expert Committee on the Classification and Staging of Rosacea