The present study showed 2 possible advantages of using TAC in the treatment of PM/DM. One is acceleration of recovery. Both PM and DM patients showed significant increases in the MMT score and significant decreases in serum CK 1 to 3 months after starting TAC compared with before. In a patient with CADM obvious improvement of skin symptoms was seen 1 month after starting TAC. Considering that some of the clinical manifestations and laboratory data suggestive of active disease, such as muscle weakness, skin symptoms and elevated levels of serum CK, worsened or remained unimproved in all of the patients even with oral PSL alone at the same dosage for at least 1 month, commencement of TAC may have produced additional therapeutic effects on PM/DM. Few case reports have so far described such clinical efficacy of TAC in PM/DM [14–16], and the present study first demonstrated it in a series of patients. The MMT score in some PM patients fluctuated even while they were being treated with PSL and TAC, and full recovery of muscle strength was more frequently seen in DM than in PM. These results suggest that TAC may be more effective for patients with DM than for those with PM.
The other possible advantage of using TAC in the treatment of PM/DM is early and rapid reduction of corticosteroid. As oral PSL, which is often used as a kind of corticosteroid, frequently causes adverse events such as osteoporosis and compression fracture of the spine, long-term use of it should be avoided if possible, particularly in postmenopausal women. Coadministration of TAC can probably enhance immunosuppressive potential and may be able to shorten the period of high-dose corticosteroid therapy. In the present study both PM and DM patients showed significant decreases in the daily dosage of oral PSL 3 to 6 months after starting TAC compared with before. These results suggest that additional use of TAC may be able to actually reduce the daily dosage of PSL without worsening of clinical symptoms and laboratory data. PSL could be maintained at a low dose after adding TAC upon recurrence in 2 PM and 1 DM patients with serious complications ascribable to corticosteroid, such as progressive osteoporosis. These PM/DM patients also showed favorable therapeutic outcomes. Coadministration of TAC in PM/DM may be able to contribute not only to dose reduction of PSL but also to improvement of symptoms and normalization of serum CK even under low-dose PSL, particularly in cases with corticosteroid-induced complications in the long clinical course. The present study is, however, a retrospective uncontrolled one in a single center. To more clearly show the therapeutic effects of TAC in PM/DM, a randomized controlled multi-center study in a larger set of patients is necessary.
TAC sometimes causes various adverse events, such as renal dysfunction and diabetes mellitus, which depend on its blood concentration [17, 18]. We, therefore, usually adjust the daily dosage of TAC based on the trough concentration in order to avoid adverse effects due to this drug. In the present study the daily dosage of TAC was 1.5 mg to 3.0 mg, and no serious adverse events occurred in any patients under a trough concentration of at most 6 ng/mL. According to recent reports, adverse effects of TAC can be adequately avoided by keeping the trough value less than 10 ng/mL [19, 20]. TAC might be safely usable at or below 3 mg/day, which is officially approved as a standard dose, in PM/DM without frequent monitoring of the trough concentration as long as renal function is almost normal. We can expect potent therapeutic effects from TAC by giving the whole dose at one time as done in this study because the trough concentration is more definitively increased than when administered in a divided dose [21–23]. CyA is also an immunosuppressive agent which acts as a calcineurin inhibitor , but frequent adjustment of the dose according to the trough concentration is sometimes necessary in order to increase therapeutic effects and prevent adverse events. TAC might be superior to CyA with regard to the lack of need for frequent monitoring of the trough concentration, particularly when using these drugs in the outpatient clinic.