Method: Skin biopsies were processed conventionally and examined in a JEOL 1011 transmission electron microscope. MMP-9 expression was detected immunohistochemically. Results: LP pemphigoides demonstrated intact basal keratinocyte cell membrane, and the lamina densa lining blister cavity correlating with moderate basal MMP-9 expression of weak intensity. Hypertrophic type demonstrated good preservation of keratinocytes and their junctions along with strong basal and suprabasal MMP-9 expression of moderate intensity. Both types demonstrated diffuse and strong MMP-9 immunostaining in dermal lymphohistiocytic infiltrate. A hypertrophic type revealed an increase of expression within dermal sweat glands comparing with LP pemphigoides. A diffuse and strong epidermal and follicular MMP-9 staining was noticed in follicular variant of LP. Conclusion: Ultrastructurally keratinocyte involvement displays deviations in various types of LP, and these changes correlate with levels of gelatinolytic activity caused by MMP-9. Objective: Clevudine is a recently introduced anti-viral agent that shows efficacy against hepatitis B virus related chronic liver diseases. However, it has been reported that certain patients who have received long-term administration of clevudine exhibit myopathy involving mitochondrial abnormalities. To make a differential diagnosis congenital mitochondrial myopathy and drug induced mitochondrial myopathy, we investigate ultrastructural findings of drug induced myopathy. Method: We studied histopathological features of myopathy focused on the various ultrastructural mitochondrial abnormalities found in 18 patients with long-term clevudine therapy. Results: In every case, ragged red fibers and multinucleated fibers with eosinophilic granules were observed. Additionally, type 2 fiber atrophy was found in 6 cases. Mainly concentrated in subsarcolemmal or inter-fibrillar areas, the abnormal mitochondria were enlarged and swollen, showing a variety of morphological types. Most of the abnormal mitochondria indicated structural abnormalities in cristae, including the apparent decrease in the number, concentric lamellar pattern, and structure that is branched or lattice-like. Conclusion: From the overall analysis, clevudine-induced myopathy is characterized by ragged fibers showing proliferation of abnormal mitochondria with various forms of inclusion bodies and abnormal cristae. Another particular feature of interest is the presence of multinucleated fibers, which, in most cases, are filled with abnormal mitochondria.