Background/Purpose:  Orbital myositis (OM), an inflammatory disease affecting the extra-ocular muscles, typically presents in the third decade.  It more commonly affects females and is extremely rare in children.  Pediatric orbital inflammatory disorders account for 6-17% of the total orbital inflammatory disorders and OM specifically makes up about 8% of pediatric orbital inflammatory disease.  Because of the rarity of pediatric OM, many questions remain unanswered and specific laboratory markers of disease activity have not yet been identified, often resulting in a protracted course.  The objective of this study is to describe the course of OM in children and to identify potential reliable indicators of disease activity.

Methods:  After obtaining IRB approval, a retrospective review was performed of all patients with a diagnosis of OM presenting between 2006 and 2012 to the Cure-JM Program of Excellence of The Ann and Robert H. Lurie Children’s Hospital of Chicago.  Duration of untreated disease (DUD) was defined as time, in months, from onset of first symptoms to the date of the first medication.   Data for muscle enzymes, neopterin, and absolute level of CD3-CD56/16+ natural killer cells (NK) via flow cytometry were determined using standard methods in the Diagnostic Immunology Laboratory.  In addition, frozen sera were tested for immunoglobulin G 4 (IgG4) levels.

Results:  Of the 4 cases, 2 were female and all were Caucasian; the mean age of onset of the first symptom was 14.4±1.2 years, and the mean DUD was 0.28±0.26 months.  One child was seen after diagnosis, treatment, and resolution of disease.  At diagnosis/first visit of the 3 active children, muscle enzymes were tested and the means are as follows (n=3 except where noted): CPK: 97.3±44.2, aldolase: 8.5±2.8 (n=2), ALT: 13±2.8 (n=2), AST: 21.3±2.9, LDH: 176±52.4.  Their mean WBC was 10.4±1.3 (n=2), mean ESR 6±4, mean neopterin: 6.3±0.14 (n=2); mean Von Willebrand Factor Antigen:  133±14.1 (n=2). The mean for IgG4 was 87.7±66  (normal range=8-89 mg/dl).  The mean NK was 96.7±28.7 at diagnosis/first visit of the 3 active subjects (lower limit of normal =138) which increased to normal range 163±57.2 with resolution of active disease.  Computed tomography studies with contrast document involvement of left superior oblique, right superior oblique, left medial rectus, left lateral rectus, and right lateral rectus muscles in the 4 children.  Only 1 child had multiple orbital muscles involved concomitantly.  Treatment was initiated with high dose intermittent pulse methylprednisolone supplemented by daily oral prednisone (0.5 mg/kg) on non-IV day as well as methotrexate (n=2) and other steroid-sparing agents. Three of the 4 children returned to normal baseline after treatment completion. The fourth child was followed in another part of the country.

Conclusion:  OM does occur in children and disease activity was not associated with creatine kinase, aldolase, neopterin, sedimentation rate, or C reactive protein values, which typically remained within normal range.  In contrast, initially decreased absolute NK trended toward normal ranges as the inflammation improved.  We speculate that this lymphocyte subset may contribute to the inflammatory myopathy.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/decreased-cd3-cd16cd56-natural-killer-cell-counts-are-associated-with-disease-activity-in-children-with-orbital-myositis/