I think you should reconsult with your doctor and rule out the other causes of a perianal rash - which could be the cause of your symptoms.
There could be several causes for the symptoms you are having. You should reconsult with your doctor to rule out the following possible causes -
'Perfumes, chemicals, or dye on toilet paper can cause an allergic reaction.
Moisture from sweat or diarrhea may cause itching. If the anal skin stays wet, the skin begins to break down.
Some foods irritate the anus when they are expelled during a bowel movement. The most common culprits are caffeine, chocolate, beer, nuts, dairy products, and spicy food.
Infections such as pinworms, yeast, and genital warts can cause itching.
Hemorrhoids, which cause painful swelling of blood vessels in the anal area, can cause itching.
Cancer, in rare instances, may be a cause.'
There are certain factors which predispose to the risk of developing anal itching as a symptom.
'Factors that put people most at risk for anal itching are as follows:
Recent antibiotic use
Chronic dry skin conditions such as psoriasis and seborrhea
Do discuss these with your doctor and exclude any possible causes in your case.
If your doctor advises you could go ahead with the biopsy - but it would be a better option to try and see if itraconazole helps with your symptoms.
Post us if you need any further information and let us know about how you are doing.