A 44-year-old male patient complains of fatigue and headache, limb numbness, dry mouth, burning and pain in the tongue. Objectively: skin and oral mucosa are pale. There are painful cracks in the corners of mouth. Dorsum of tongue is smooth, glossy, with bright red striae. Blood count: Hb- 70 g/l, RBCs -1,5 × 1012/l, colour index -1,6, leukopenia, thrombocytopenia, lymphocytosis. What is the most likely diagnosis?