Minocycline for the treatment of sarcoidosis: is the mechanism of action immunomodulating or antimicrobial effect?

A 47-year-old female was diagnosed to have pulmonary, ocular, and nodular-type muscular sarcoidosis. Seven years later, nodules developed in all limb muscles. She received minocycline 200 mg daily, which resulted in an obvious reduction of the muscular sarcoidosis with a significant decrease in the serum angiotensin-converting enzyme level. Nine months later, the minocycline was discontinued, thus resulting in a rapid recurrence of the disease. The immediate readministration of minocycline again resulted in a prompt improvement. We detected Propionibacterium acnes within the granulomas in the affected muscle by an immunohistochemistry. More interestingly, we found a decrease in the circulating levels of interleukin-12 p40 and interferon-inducible protein-10 during the minocycline therapy. The minocycline therapy may be effective for sarcoidosis and the fact that the disease rapidly relapsed after discontinuation of the minocycline administration suggests that the mechanism of action in this case may be immunomodulating but not antimicrobial effect.