Prevalence and clinical characteristics of adult polymyositis and dermatomyositis; data from a large and unselected Norwegian cohort.

OBJECTIVES: The occurrence of polymyositis (PM) and dermatomyositis (DM) in the general population is largely unknown and unbiased data on clinical and laboratory features in PM/DM are missing. Here, we aim to identify and characterise every PM/DM patient living in southeast Norway (denominator population 2.64 million), 2003-2012. METHOD: Due to the structure of the Norwegian health system, all patients with PM/DM are followed at public hospitals. Hence, all public hospital databases in southeast Norway were screened for patients having ICD-10 codes compatible with myositis. Manual chart review was then performed to identify all cases meeting the Peter & Bohan and/or Targoff classification criteria for PM/DM. RESULTS: The ICD-10 search identified 3160 potential myositis patients, but only 208/3160 patients met the Peter & Bohan criteria and 230 the Targoff criteria (100 PM, 130 DM). With 56 deaths during the observation period, point prevalence of PM/DM was calculated to 8.7/100 000. Estimated annual incidences ranged from 6 to 10 /1 000 000, with peak incidences at 50-59 (DM) and 60-69 years (PM). Myositis specific antibodies (Jo-1, PL-7, PL-12, signal recognition particle (SRP) and Mi-2) were present in 53% (109/204), while 137/163 (87%) had pathological muscle MRI. Frequent clinical features included myalgia (75%), arthritis (41%) dyspnoea (62%) and dysphagia (58%). Positive anti-Jo-1, present in 39% of DM and 22% of PM cases, was associated with dyspnoea, arthritis and mechanic hands. CONCLUSIONS: Our data indicate that the population prevalence of PM/DM in Caucasians is quite low, but underscores the complexity and severity of the disorders.

Long-term experience with rituximab in anti-synthetase syndrome-related interstitial lung disease.

OBJECTIVE: To retrospectively evaluate the efficacy and safety of rituximab (Rtx) treatment in patients with anti-synthetase syndrome (ASS) and severe interstitial lung disease (ILD). METHODS: Patients with severe ILD and >12 months follow-up post-Rtx were identified from the Oslo University Hospital ASS cohort (n = 112). Clinical data, including pulmonary function tests (PFTs), were retrospectively collected from medical reports. Extent of ILD pre-, and post-Rtx was scored on thin-section high-resolution CT (HRCT) images and expressed as a percentage of total lung volume. Muscle strength was evaluated by manual muscle testing of eight muscle groups (MMT8). RESULTS: Altogether, 34/112 ASS patients had received Rtx; 24/34 had severe ILD and >12 months follow-up post-Rtx (median 52 months). In these 24 patients, the median percentage of predicted forced vital capacity, forced expiratory volume in 1 s (FEV1) and diffusing capacity of the lungs for carbon monoxide (DLCO) increased by 24%, 22% and 17%, respectively, post-Rtx. Seven patients (all with disease duration <12 months and/or acute onset/exacerbation of ILD) had >30% improvement in all three PFTs. HRCT analysis showed a median 34% reduction in ILD extent post-Rtx. MMT8 score increased post-Rtx. During follow-up, 7/34 (21%) Rtx-treated ASS patients died; 6/7 deaths were related to infections. The mortality rate in the Rtx-treated group was comparable to that of the remaining ASS cohort (25/78 deceased; 32%). CONCLUSION: This study, which included 24 Rtx-treated ASS patients with severe ILD, reports improved PFTs after a median 52 months follow-up post-Rtx. The best outcome was observed in patients with a disease duration <12 months and/or acute onset/exacerbation of ILD. The study indicates that Rtx could be a treatment option for selected ASS patients, but infections should be given attention.

Rituximab treatment of the anti-synthetase syndrome: a retrospective case series.

OBJECTIVE: Interstitial lung disease (ILD) is the major determinant of morbidity and mortality in the anti-synthetase syndrome (ASS). Here we have retrospectively assessed 11 ASS patients with ILD treated with the anti-CD20 mAB rituximab at our tertiary referral hospital. METHODS: Data on clinical and laboratory parameters, lung imaging by high-resolution CT thorax and pulmonary function tests were collected from patient examinations done up to 6 months before rituximab was initiated, and at 3 and 6 months post-treatment. RESULTS: All the 11 ASS patients had severe and progressive ILD and most of them had previously failed on cyclophosphamide and/or other immuno-modulating agents. Rituximab appeared to stabilize and/or improve the ILD in 7 of 11 ASS patients during the first 6 months after treatment. The rituximab treatment appeared to decrease the serum level of anti-Jo-1 antibodies, but the decrease was most often modest. One patient developed a fatal infection 3 months after the last infusion with rituximab. In the other ASS patients, the treatment was well tolerated. CONCLUSIONS: This retrospective case series indicates a short-term beneficial effect of rituximab in ASS. Prospective, controlled studies are needed to validate this finding and further assess safety issues.