Amyloid in a patient with Reiter's syndrome - secondary or coincidental? Differentiation with potassium permanganate

A patient with Reiter's syndrome developed a pulmonary nodule composed of amyloid. Reiter's syndrome has been reported as 1 of the diseases associated with secondary systemic amyloidosis. Isolated nodular pulmonary amyloid has not been reported to become systemic. Potassium permanganate treatment of amyloid abolishes congo red stain affinity for amyloid of unknown origin found in secondary amyloidosis. However, the amyloid of immunoglobulin origin, characteristic of primary amyloid, is resistant to KMnO4. The amyloid deposit from our patient was resistant to KMnO4 which suggested that the pulmonary amyloid was a coincidental nodular amyloid deposit in the lung rather than secondary amyloidosis.