Muscle biopsy is must for making diagnosis of polymyositis (PM) or inclusion body myositis (IBM). This is because there are several mimickers of PM and IBM, which can be confused with myositis. Metabolic myopathies, muscle dystrophies and endocrinopathies are commonly misdiagnosed as PM or IBM. Moreover, muscle biopsy is must to differentiate between PM and IBM. In cases where muscle biopsy is not feasible, presence of PM-associated myositis autoantibodies (like anti-signal recognition particle (anti-SRP), antisynthetase antibody, etc.) can be helpful in making a probable diagnosis of PM. In dermatomyositis (DM) although muscle biopsy is very helpful and should be performed whenever it is feasible, muscle biopsy is not critical to the diagnosis especially in the presence of characteristic DM rashes like Gottron’s papules, heliotrope rash. This is because of characteristic rash of DM has very high specificity.

Yes. Histopathology in myositis has prognostic value. For example, cases without much degeneration and/or regeneration with mild inflammation (if biopsy was done before starting treatment) are a good prognostic marker and hopefully patient will require less aggressive regimen. On the other hand, patients with severe myonecrosis or myophagocytosis especially if these features are observed in the absence or subtle inflammation are characteristic of necrotizing myopathy that has worse prognosis. Moreover, patients with necrotizing myopathy one should look for paraneoplastic causes or statin-induced necrotizing myopathy (anti-HMGCR antibody positivity) or anti-SRP antibody positivity. These patients often require early aggressive regimens. Severity of atrophy on histopathology is also very helpful as it indicates muscle damage, which may not respond to immunosuppressive treatment.

Despite the lack of placebo-controlled trials, glucocorticoids are considered the mainstay of initial treatment of IIM as they normalize serum muscle enzymes and improve or preserve muscle strength. Few patients with milder disease and good prognostic features can be treated with glucocorticoid monotherapy; however, most of the patients will require the addition of another immunosuppressive drug like methotrexate or azathioprine due to refractory disease, disease flares or to minimize glucocorticoid side-effects. In almost all patients, we recommend starting of methotrexate or azathioprine concomitantly at initiation of glucocorticoids unless contraindication.

Patients who are severely ill (marked weakness, severe dysphagia, or rapidly progressive interstitial lung disease) should be given pulse intravenous methylprednisolone (1000 mg daily for three consecutive days) followed by the high-dose oral glucocorticoid regimen noted above in combination with a second-line immunosuppressive drug.
We recommend starting prednisone at a dose of 1 mg/kg per day, often in divided doses and generally not exceeding 80 mg daily. After 4–6 weeks of high-dose therapy, prednisone is slowly tapered to the minimum effective dose using the general guideline of tapering the existing dose by 20–25% monthly. When prednisone dose reaches 5–10 mg/day the tapering is generally held for total dose of prednisone to be 9–12 months.

Unfortunately, there are no studies done on upfront rituximab and MMF in myositis. Although, it seems a good hypothesis it needs to be confirmed by clinical trials. Current evidence of rituximab in myositis only support’s its use when first and second-line therapies fail and there is no evidence of it to be a first-line drug. In the largest clinical trial of rituximab in IIM [Rituximab in Myositis (RIM) trial] that we recently completed all patients refractory to glucocorticoid therapy (or at least one immunosuppressive agent) were randomized to receive two 1 g rituximab infusions either at baseline or 8 weeks later. Although the group treated earlier demonstrated no faster response to therapy than group treated later (thus failing to meet the primary outcome), the definition of improvement was met by 83% patients with a median time to achieving the definition of improvement of 20 weeks. Rituximab also showed a significant steroid-sparing effect and the mean dose of prednisone decreased from 21 mg at baseline to 14 mg daily at the end of the study. Moreover, patients retreated with rituximab after a disease flare also responded to retreatment.

I don’t think there is much role of hydroxychloroquine in PM alone. But, there is definite role of hydroxychloroquine in mild DM when skin is the main troublesome symptom. There is evidence that skin reaction to hydroxychloroquine and DM rash exacerbations might be more with hydroxychloroquine in DM patients, but it is still a good option in many patients with mild DM. CTD-associated myositis hydroxychloroquine should be primarily used for the associated CTD and there is no need to avoid hydroxychloroquine in these patients.

Generally, immunosuppressive drug is given for about 2 years in a patient with average prognosis and response. In a few patients with mild disease and good prognostic features, it can be shortened to 1 year, whereas in patients with severe disease and/or poor prognostic features, it should be continued for 3–5 years. Steroid-free remission is definitely possible in IIM and is currently a usual goal of therapy. Apart from 20–30% of patients who are refractory, most IIM patients can achieve steroid-free remission in IIM.

Currently, there are no existing guidelines on screening of malignancies in dermatomyositis patients. We recommend age-appropriate screening in patients with good prognostic features. This includes basic laboratory tests like CBC, renal and liver function tests, sedimentation rate, chest X-ray, colonoscopy in both male and female, with addition of mammogram, Pap smear, vaginal ultrasound in female and serum PSA in males. In patients with high-risk, a chest, abdomen, pelvis CT is recommended at initial diagnosis. Anti-TIF1g antibody will be useful test in near future for risk stratification of the DM patients.

Main long-term morbidity of corticosteroid in IIM include diabetes, eye problems like cataract and glaucoma, osteoporosis, steroid myopathy, weight gain, cushinosis and infections. The main way to reduce this steroid complication is to start a non-steroid immunosuppressive agent concomitantly with glucocorticoids at the diagnosis and faster tapering of steroid to a low-dose of 5–10 mg if steroid side-effects are observed in a patient.

Myositis specific autoantibodies are very useful in myositis in diagnosis, prognosis, risk stratification as well as management. Antisynthetase antibody positivity (anti-Jo1 and non-Jo1 antibodies) or anti-MDA5 antibody should be treated aggressively with monitoring of ILD and PAH. Anti-SRP and anti-HMGCR antibody patients should also be treated aggressively. Whereas patients with anti-Mi-2 could be take less aggressive regimen. Patients without myositis-specific autoantibodies should be reviewed carefully for non-myositis myopathies as they are common mimickers and generally first clue is non-responsiveness to immunosuppressive drugs. Patients with Anti-TIF1g antibody should be screened thoroughly for cancer.

At first visit after a rheumatologist has confirmed the diagnosis, patients should be told that the myositis treatment is available and most patients will go into remission or low disease activity state on appropriate treatment. They should also be told that this is a serious life-threatening condition with a significant long-term morbidity and disability if untreated. This condition should be treated appropriately by rheumatologist with regular follow-up and will take time to respond as well as usual treatment is about 1–2 years.