To diagnose guttate psoriasis, the doctor will usually refer a person to a specialist skin doctor called a dermatologist. The dermatologist will examine the affected areas of skin and take a complete medical history to rule out other possible conditions.
A dermatologist may order a skin biopsy, which is a procedure that involves taking a small sample of skin and sending it to a lab for testing. This will help rule out any other possible reasons for the skin problems. It will also help a dermatologist work out which type of psoriasis a person has.
A dermatologist can usually diagnose tinea versicolor by looking at a person's skin. If they are unclear on the diagnosis, they may scrape off a bit of skin to examine under a microscope. Alternatively, they might examine the skin using a Wood lamp, which is a diagnostic tool that emits a specific type of light. A doctor can make a diagnosis if the affected skin appears yellowish-green when looked at it under the lamp.
The type of treatment a doctor prescribes depends upon the type of psoriasis a person has, its location, and any other complicating factors.