A 36-year-old computer engineer came to the clinic complaining of itchy and scaly fingernails chipped and fell off easily. It started ten years ago, is getting worse, and all of his fingernails are affected. The nails are not painful but do not look normal. He had patches of dry, scaly skin on his scalp and low back. He denies taking medication and his family history was unremarkable. His physical examination reveals a pink area with scale on his left temporal scalp, as well as other patches on his back. The majority of the nails were intact but had some proximal erosion; some nails had separation from the nail bed, as well as scaling and yellowing distally. However, most of the nails had pitted, with the periungual area intact, as is shown in the image below. Which of the following is the most likely diagnosis,