Abstract
BackgroundThe autophagic vacuolar myopathies (AVM) are a group of inherited myopathies defined by the presence of autophagic vacuoles in pathological muscle specimens. AVM can be categorized into three groups: acid maltase deficiency, myopathies characterized by autophagic vacuoles with unique sarcolemmal features, and rimmed vacuolar myopathies (RVM). While the pathogeneses of these conditions are still being elucidated, some drugs (e.g., chloroquine, its analog, hydroxychloroquine, and colchicine) can also cause AVM. Minocycline is a disease-modifying anti-rheumatic drug that may be used in the treatment of rheumatoid arthritis (RA). Here, we describe the first case of minocycline-associated AVM with rimmed vacuole formation.Case presentationA 75-year-old woman suffering from RA has been continuously treated with minocycline (200 mg/day) for the past 7 years. During this time, she developed a myopathy that predominantly affected her lower limbs. Histological studies of biopsied muscle revealed scattered atrophic myofibers with rimmed vacuoles that contained pigment granules. Histochemical staining revealed that the pigment comprised both iron and melanin, which is consistent with type II minocycline-induced cutaneous pigmentation. Under electron microscopy, autophagic vacuoles were consistently observed in association with numerous collections of pigment granules.ConclusionsThis is the first report of minocycline-induced pigmentation in skeletal muscle. The strong association between autophagic vacuoles and the accumulation of minocycline-induced pigments suggest that long-term minocycline treatment induced pigment accumulation, leading to elevation of autophagic activity and RVM. It might also be possible that minocycline directly activated autophagy, as the observed pigments are known to form complexes containing minocycline and/or its metabolites. As long-term minocycline treatment is expected to be used more widely in the future, we must draw attention to this adverse effect.
Highlights
The autophagic vacuolar myopathies (AVM) are a group of inherited myopathies defined by the presence of autophagic vacuoles in pathological muscle specimens
The strong association between autophagic vacuoles and the accumulation of minocycline-induced pigments suggest that long-term minocycline treatment induced pigment accumulation, leading to elevation of autophagic activity and rimmed vacuolar myopathies (RVM)
Autophagy, which is a lysosomal degradation pathway that is essential for cell survival [1], plays a key role in the pathogenesis of several inherited myopathies; these include autophagic vacuolar myopathies (AVM) [2] as well as the drug-induced AVM caused by chloroquine, hydroxychloroquine and colchicine [3,4]
Summary
Minocycline has proven to be an effective diseasemodifying anti-rheumatic drug. We report for the first time that long-term minocycline treatment may cause RVM via the accumulation of minocycline-induced pigmentation in skeletal muscle. The clinical features of minocycline-associated RVM are very similar to those observed in hydroxychloroquine myopathy, suggesting that there may be a common pathogenic mechanism underlying these conditions. As long-term minocycline treatment may be used more widely in the future, we must draw attention to this adverse effect. Consent Written informed consent was obtained from the patient for publication of this case report. A copy of the written consent is available for review by the Editor-In-Chief of this journal. Competing interests The authors declare that they have no competing interests. All authors read and approved the final manuscript
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