SHM Converge Scientific Abstract ePoster Gallery-Antibody Negative Juvenile Polymyositis Presenting as Knee and Lumbar Pain

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This case describes a 6-year-old girl who initially presented with 2 weeks of bilateral knee pain and was discharged with supportive care. Over the following weeks, her symptoms worsened to diffuse body aches, back pain, weakness, difficulty standing and walking, and falls, prompting evaluation in the emergency department.<br /><br />Her laboratory studies showed markedly elevated creatine kinase (CK 5000), AST 200, and ALT 100, suggesting muscle injury. Respiratory viral testing was negative, and x-rays of the hips and knees were reassuring. Because of progressive weakness and difficulty ambulating—important “red flag” symptoms in children with musculoskeletal pain—she underwent a broader neurologic and rheumatologic workup.<br /><br />Further evaluation included MRI studies of the brain, cervical spine, pelvis, and thighs. Imaging of the pelvis and thighs showed muscle inflammation consistent with myositis. Muscle biopsy demonstrated perifascicular muscle atrophy and necrosis, supporting polymyositis. Although myositis-specific and myositis-associated antibody panels were negative, autoimmune myositis was still strongly suspected. Additional testing, including HMGCR antibody testing, was also negative.<br /><br />She was treated with high-dose IV methylprednisone for 3 days, followed by IVIG, then transitioned to oral prednisone and methotrexate. Rheumatology and Neurology followed her during admission and after discharge. Over the next few months, she had complete resolution of symptoms.<br /><br />The case highlights that juvenile polymyositis can present atypically with knee and back pain before progressing to severe weakness and gait impairment. In children with musculoskeletal pain, weakness, fatigue, or difficulty walking, prompt full evaluation is essential. Negative antibody testing does not exclude autoimmune myositis, and improvement with steroids and IVIG can support the diagnosis.

Asset Subtitle

Nicole D. Nammour

Meta Tag

Author List Nicole D. Nammour

Category Clinical Vignettes

Concept Juvenile Polymyositis

Concept Weakness

Concept Ambulatory Dysfunction

Concept Progressive Weakness

Concept Creatine Kinase

Distinguished Non-Finalist

Presenter Organization University of Tennessee Health Sciences Center

Presenting Author Nicole D. Nammour

Track Pediatric

Keywords

juvenile polymyositis

myositis

muscle weakness

elevated creatine kinase

knee pain

back pain

MRI myositis

muscle biopsy

IV methylprednisone

IVIG

Juvenile Polymyositis

Weakness

Ambulatory Dysfunction

Progressive Weakness

Creatine Kinase