A 35 year old man presents with progressive breathlessness. He gave a history of polyarthralgia with painful lesions on the shin. CXR: bilateral hilar lymphadenopathy. What’s the most likely diagnosis?

The key is C. Sarcoidosis. [Sarcoidosis is a granulomatous inflammatory disease that affects multiple organs in the body, but mostly the lungs, skin and lymph glands. Given case is termed as Lofgren’s syndrome. Lofgren's syndrome is an acute form of sarcoidosis characterized by erythema nodosum, bilateral hilar lymphadenopathy, and polyarthralgia or polyarthritis.