A full skin exam should be undergone to investigate other areas psoriasis might manifest including places like the scalp or nails. Psoriasis can be very hard to diagnose because it sometimes looks like other skin diseases such as eczema. So a doctor may take a biopsy to look at a small sample of your skin under a microscope to see if psoriasis is the cause of your skin condition. Definitively you are likely to be referred to a dermatologist as they specialize in skin conditions and should be best placed to determine a diagnosis and treatment plan for you. You might also see an internist who diagnoses and treat as a wide range of conditions and are especially involved in the ongoing care of chronic illnesses, such as myself, for certain types of psoriasis. You might need to see other healthcare professionals as well, such as a rheumatologist. If you have psoriatic arthritis, a rheumatologists would be the best person to diagnose this type of arthritis as you have many other symptoms. And this arthritis can be confused with other types of rheumatological conditions as well.