Q. A 32-year-old man is brought to the emergency department by his wife for worsening back and right knee pain for the past four days. But since morning he has been unable to walk due to the sudden onset of left heel pain. He also complains of a new-onset nonpruritic rash on the chest and congestion of the eyes since yesterday. On further questioning, he says that all his problems started 1 week ago with loose watery diarrhea and there is an outbreak in the fast food center where he works. He doesn’t have fever, abdominal pain, or urinary problems. He is taking over-the-counter painkillers and oral rehydration supplements. Family history shows that his sister has lupus and is taking treatment. His temperature is 98.8°F (37.1°C), pulse is 88 beats per minute, BP is 110/70 mm of Hg and respiratory rate is 14/min. Physical examination shows bilateral conjunctivitis and small erythematous scaly plaques over the anterior chest, soles, and palms. Oral examination shows mucosal ulcerations on the sides and tip of the tongue. Joint examination shows mildly swollen warm tender sacroiliac joints and right knee joint and there is diffuse inflammation at the site of insertion of the left Achilles tendon. What is the most likely diagnosis for this patient based on his clinical features?