Nonspecific Orbital Inflammation

Nonspecific orbital inflammation (NSOI) is a term used to describe nonmalignant inflammation of the orbit characterized by a polymorphous lymphoid infiltrate with varying degrees of fibrosis, without a known local or systemic cause. The emphasis is on lack of finding a known cause. Orbital inflammation itself is not a diagnosis, but rather a description of a tissue response to some underlying problem, such as infection, irritation, or injury, which has triggered the immune system. The injured cells release chemical factors stimulating the inflammatory response which is characterized by symptoms of pain, redness, swelling, warmth, and possible dysfunction of the tissues involved. In the case of the orbit, it is infiltration of orbital soft tissues by chronic inflammatory cells that causes findings such as proptosis, eyelid swelling, chemosis, pain, diplopia, or visual loss. Every effort must first be made to identify a specific cause of the inflammation. Navigating through the differential diagnosis of diseases that can cause or simulate orbital inflammation is challenging; however, adhering to a methodical history and exam will help facilitate the process. Only once all other specific etiologies have been eliminated can one conclude with the diagnosis of nonspecific orbital inflammation, which only means that the causative pathogen or trigger could not be identified.