A 18 years boy, not responding to the treatment of psoriasis with methotrexate and other drugs, c/o extreme weakness and wasting of thigh muscles, that he CAN'T sit on the floor comfortably, and can't get up also. On examination, heart rate is high with sometimes palpation, tremors in hand like hyperthyroidism, no pain in knees, ankles.

What other diseases/conditions may be associated with severe psoriasis in this case?