Can a biopsy showing AGA be wrong?

Can a biopsy of AGA be wrong?

I'm often asked if a biopsy can be 'wrong.' The short answer is that yes, a biopsy can potentially be wrong. Biopsies are simply "samples" and used to represent a larger area. However,  the long answer is that if a biopsy is done properly and from the right area, and read by a good pathologist, them no, it is very likely that if a biopsy returns showing that androgenetic alopecia is one of the diagnoses that this is correct. The identification of vellus hairs and a terminal to vellus hair ratio of less than 4:1 with telogen hairs less than 15% is typical of androgenetic alopecia. Many individuals (especially women) with androgenetic alopecia do not have a family history so this fact should not be given too much emphasis.

A biopsy can "sometimes" be wrong in these situations:

1. Diagnoses of Scarring Alopecia (Lichen planopilaris, Folliculitis Decalvans)

2. Some diagnoses of Telogen Effluvium

3. Some diagnoses of Alopecia Areata

Most of the time, of course, a biopsy is correct in these situations. However, there are many cases alopecia areata, telogen effluvium and scarring alopecia that are challenging. A biopsy is just a piece of the puzzle and one must put together all the facts from the clinical history. examination, blood test results to come up with the diagnosis. 

A biopsy is less likely to be 'wrong' in these situations

1. Androgenetic alopecia (especially with use of horizontal sections)

2. Tinea Capitis

3. Trichotillomania

4. Skin Cancers and Metastases