A 41-year-old patient cosulted a dermatologist about discoloration, thickening, brittleness of toenails. These symptoms have been present for about five years. Objectively: nail plates in all toes are thickened, of dirty yellow color, lustreless, crumble over the edge. Microscopy of the nail plate material treated with alkali revealed mycelial filaments. Material inoculation onto Sabouraud medium resulted in growth of the Trichophyton rubrum colony. What is the most likely diagnosis?