Session Type: Abstract Submissions (ACR)
Background/Purpose: We examined demographic, clinical and laboratory features of juvenile polymyositis (JPM) and muscular dystrophy in children to improve classification of these two conditions.
Methods: Thirty-nine patients with probable or definite JPM (31 JPM and 8 JPM overlapping with another connective tissue disease) by Bohan and Peter criteria and 9 patients with various muscular dystrophies (1 Duchenne’s carrier, 8 limb girdle dystrophies) were examined. Differences in demographic and clinical features (including musculoskeletal, cutaneous, gastrointestinal, pulmonary, cardiac, constitutional signs and symptoms), muscle enzyme levels, Magnetic Resonance Imaging (MRI), electromyography (EMG), and muscle biopsy features between patients with JPM and dystrophies were evaluated by Fisher’s exact and Rank sum tests. Backwards step-wise logistic regression modeling, followed by exact logistic regression, was performed to examine significant univariable differences between JPM and dystrophies in a multivariable model.
Results: Delay to diagnosis was longer in patients with dystrophies (median 12.0 months) compared with JPM (median 4.0 months, respectively, p=0.03). In addition, the following demographic, clinical and laboratory features distinguished JPM and dystrophies:
|African-American Race||17/39 (43.6)||0/9 (0.0)||0.018|
|Insidious illness onset (› 6 mo from first symptom to diagnosis)||11/31 (35.5)||7/9 (77.8)||0.05|
|Muscle atrophy on exam||17/37 (45.9)||8/9 (88.9)||0.027|
|Muscle atrophy on MRI||4/21 (19.0)||5/6 (83.3)||0.008|
|Increased insertional and spontaneous activity/fibrillation potentials on EMG||17/18 (94.4)||5/9 (55.6)||0.03|
|Complex repetitive discharge on EMG||16/23 (69.6)||2/9 (22.2)||0.02|
|Diffuse variation of myofiber size on muscle biopsy||20/38 (52.6)||9/9 (100.0)||0.008|
|Fiber hypertrophy on muscle biopsy||3/38 (7.9)||4/9 (44.4)||0.018|
|Myofiber fibrosis on muscle biopsy||4/38 (10.5)||5/9 (55.6)||0.007|
|Absence of response to treatment with prednisone||2/39 (5.1)||3/9 (33.3)||0.039|
|Absence of response to treatment with other immunosuppressive agents||2/39 (5.1)||4/9 (44.4)||0.008|
Other features did not differ between JPM and dystrophies, including frequency of abnormal values and levels of serum muscle enzymes (CK, LDH, Aldolase, AST, and ALT); muscle edema and fatty replacement of muscle on MRI; inflammatory features on muscle biopsy; presence of short duration, small amplitude polyphasic motor units action potentials (MUAPS) and positive sharp waves on EMG; and demographic features (age at diagnosis, family history of autoimmune disease). Examining the 8 variables that were significant on univariate analysis in backwards selection stepwise logistic regression, followed by exact logistic regression, revealed less frequent myofiber fibrosis on muscle biopsy (OR = 0.1) and onset speed (OR = 0.16) to be significant predictors of JPM vs. muscular dystrophy. Because there were no African-American patients with dystrophies, a point estimate for race could not be obtained. The final multivariable model, including myofiber fibrosis, onset speed and race, provided a sensitivity of 55.6%, specificity of 97.2%, positive predictive value of 83.3%, and negative predictive value of 89.7%.
Conclusion: Muscular dystrophy can present similarly to patients with idiopathic inflammatory myopathy, particularly polymyositis. Selected demographic, clinical, and laboratory features may be helpful in distinguishing these patients, particularly the presence of myofiber fibrosis on muscle biopsy and a slower illness onset.
J. D. Katz,
R. V. Jones,
P. A. Lachenbruch,
O. Y. Jones,
F. W. Miller,
L. G. Rider,
« Back to 2012 ACR/ARHP Annual Meeting
ACR Meeting Abstracts - https://acrabstracts.org/abstract/clinical-and-laboratory-features-distinguishing-juvenile-polymyositis-and-muscular-dystrophy-in-children/