JIIM/JDM is rare but is a well-known entity. It should be noted from the outset, that the number of notes reviewed in this study was only 5 and as such, it would be difficult to make any general statements on prevalence or incidence in our population. The authors did reach out to colleagues at another Regional Health Authority, however they reported that research was halted during the COVID-19 pandemic at that time. Nevertheless, there were certain observations that was worth reporting.
We did see a female predominance in our study (male: female ratio of 1:4) which is in keeping with most of the international literature on this disease. (9,10). Additionally, the peak age of onset is approximately 7 year (9,10) and we found an average of 6.8 years with a median age of 6 years in our study. The 5 patients were not clustered together. Additionally, there was no specific pattern of month presentation. Whilst it is recognized that there is an increasing prevalence as one moves closer to the equator, as well as increased flares in exposure to increase UV radiation (2,3), our tropical climate did not reveal any specific month of presentation or onset of disease. Meteorological data would be required to compare UV radiation in each month to make an objective assessment with a larger sample size.
In terms of environmental triggers, 40% had a previous upper respiratory tract infection in 6 months prior to presentation which is a recognized trigger for disease flares in children with JDM (2). Interestingly, there was one patient who had a past medical history of Kawasaki disease which is now a recognized risk factor for autoimmunity. In a 2020 registry-based cohort study by Danish researchers, they found that patients with previous Kawasaki disease had an increased risk of developing autoimmune diseases including dermatomyositis and polymyositis after 10 years of the disease. (11) Of note, this patient developed JIIM, 6 years after presenting with Kawasaki disease. This should make us rethink how Kawasaki disease is viewed- beyond just its cardiac sequelae. A recommendation would be to refer these children to the rheumatology service as is done in Singapore. (12)
The most common presenting complaint were skin rash and weakness which accounted for 62% of all presenting complaints. An interesting point to note is that joint pain and pruritis were the most common additional features present. However, the range of varying symptoms highlights the fact that JIIM/JDM can present with many other constitutional features. (9) In terms of pathognomonic features, Gottron’s papule and heliotropic rash were the most present feature in our JDM patients, which is usually the findings that help distinguish JDM from polymyositis. (13)
Of note, with respect to muscle enzymes, Creatinine Kinase was 5 to 6 times higher in the one child who had probable myositis by Peter and Bohan’s Criteria. This is in keeping with the fact that CK in IIM patients tend to be the higher in Juvenile Polymyositis compared to JDM. (14) This study found a 60% ANA Positivity rate which is similar to the 70% reported by Shah M. et al. (14)
Myositis Specific antibody panels and Myositis Associated Antibodies panels are not available in the public setting at SWRHA and may account for the low testing seen in the notes reviewed. However, a few notable observations on autoantibodies done from Extractable Nuclear Antigen-23 testing was discovered.
One child with probable IIM, tested positive for Anti PM and Anti Ku which can be found in myositis and systemic sclerosis overlap. (14) Another patient with probable polymyositis, was positive for Anti RP155 only, which is not one of the usual autoantibodies as identified by Rider and Nistala in their overview (1). One patient with definite JDM tested positive for 4 Autoantibodies which included: Anti Mi2 A, Anti Mi2 B, Anti RP11 and Anti RP155. Anti Mi2 is well documented as a myositis specific antibody, however, Anti RP11 and RP155 can be associated with systemic sclerosis (15). As such, it raises the question whether these 2 children with Anti RP155 positive Antibodies, may have JDM overlapping with another connective tissue disease, sometimes termed “overlap myositis” (1,16). It may also be possible that this is a new autoantibody association of JDM in a Trinidadian population. However, the study size was too small to definitively pronounce that Anti RP155 is a new myositis associated antibody in a Trinidadian population.
It is noteworthy that MRI was utilized in 60% of patients, as it offers the advantage of being non-invasive and is now being utilized more frequently by paediatric rheumatologists and dermatologists in diagnostic workup as well as in monitoring response to therapy in JIIM. (17,18) Specifically, in our study, muscle biopsy and EMG was documented in 60% of patients, which could be due to the invasiveness of these procedure. Moreover, muscle biopsy did not add much information to the diagnosis in this cohort. Additionally, our institution does not have the specialized histopathology services available to effectively report on JIIM/JDM specimens. Whilst it would be beneficial to have further trained personnel to offer this service, MRI may offer a better solution in our setting to assist in diagnosis. As such, a recommendation would be to utilize Magnetic Resonance Imaging earlier, in children being worked up for JIIM.
The diagnosis of JDM has long been based on the works of Bohan and Peters in 1975. (4) Although it still remains widely in use by residents and clinicians across the board, there have been many attempts to revamp this criterion, with the latest being the EULAR/ACR Classification of 2017. (5) The advantage of this new criteria is that it can be scored with or without a muscle biopsy recognising the shift away from invasive testing. Additionally, there is an online calculator which facilitates an easier scoring. (6) Leclair and Lundberg (19) compared sensitivities and specificities of six varying IIM criteria and found that, when compared to Peter and Bohan’s criteria, EULAR/ACR 2017 had a slightly lower sensitivity (87–93% compared with 94–98%) but much better specificity (82–88% compared with 29–55%).
A secondary analysis to compare these 2 criteria and found an 80% concordance between them. The reason for the discordance was that one child had neither an Electromyogram nor a biopsy documented in the notes. Therefore, the Peter and Bohan 1975 criteria should be continued to be utilized in clinical practice. However, in children without an EMG or a Muscle Biopsy, the EULAR/ACR 2017 offers a better classification criterion.
In terms of drugs used, all children received Methotrexate and prednisolone which is in keeping with the latest consensus guidelines as the therapeutic agent of choice to commence. (20) The only parental drugs used were Intravenous Immunoglobulin and methylprednisolone. In attempting to stratify prednisolone dosage and duration, there were gaps in the notes and this presented some difficulty to report. As such, a recommendation would be to place notes on an electronic database for easier access and analysis.
All children were prescribed physiotherapy, and 80% were on vitamin D supplementation which is in keeping with current recommendations. (20) The treatment options in this retrospective analysis at this centre were in keeping with guidelines.
With respect to clinically inactive disease at the last visit, a modified PRINTO criteria similar to that used by O’kongo et al was used. (7) 40% had clinically inactive disease by our criteria of analysis. 60% had physiological changes at last visit and one patient who had the earliest disease onset in this data set also had calcinosis. His calcinosis appeared to be unresponsive to multiple therapy. Of note, there is no established guideline on JDM calcinosis management in the literature, however a survey of paediatric rheumatologists in 2017, found that optimising immunosuppressants and adding adjunct therapies like bisphosphonates and calcium channel blockers were the top two additional therapies recommended. (21) A recommendation would be for this institution to look at establishing a protocol for adjuvant therapy- like bisphosphonates, in children with JDM as another option for intractable calcinosis.