Löfgren syndrome is an acute presentation of sarcoidosis classically presenting with bilateral hilar lymphadenopathy, erythema nodosum, oligoarthritis, and fever. 

It most commonly affects adults in their third and fourth decades, occurs more frequently in women, and is particularly prevalent in White individuals, particularly Northern European populations, where it carries a strong genetic association with HLA-DRB1*03.

The pathophysiology involves an acute immune response to environmental triggers resulting in granulomatous inflammation.  

The condition typically follows a self-limited course, with resolution over weeks to months. Complete remission usually occurs within 2 years, and chronic or relapsing disease is rare, typically including mild pulmonary abnormalities, rare uveitis, or transient metabolic disturbances. Serious cardiac, neurologic, hepatic, splenic, and fibrotic pulmonary involvement is distinctly rare.