Working Diagnosis:
Atypical Muscular Dystrophy

Treatment:
The patient was continued in physical therapy, referred to pediatric neurology for further regular examinations, and genetics/metabolism for whole exome sequencing.

Outcome:
The patient continued to play in organized athletic competitions and continues to await genetics evaluation. She will be followed regularly as an outpatient for progression of symptoms.

Author's Comments:
Myalgia may be seen in the clinic and training rooms. Further evaluation is indicated if there is decreased exercise tolerance, episodic bilateral exertional pain, nocturnal pain, fevers, new medications, dark urine, persistent symptoms, or weakness on exam are present. Acquired sources of myopathy include toxic (corticosteroids, immune checkpoint inhibitors, statins, hydroxyurea, acid blockade medications), auto-immune (Dermatomyositis, Polymyositis), infectious (Lyme Disease, HIV, Coxsackie B), endocrinologic (Cushing's Disease, hypothyroidism, hyperthyroidism), nutritional (vitamin D deficiency), and paraneoplastic.1 In children and adolescents, inherited causes must be considered as well. The inherited etiologies include inborn errors of metabolism (Glycogen Storage Diseases, Fatty Acid Oxidation Defects, MELAS, Leber hereditary optic neuropathy), muscular dystrophy (Becker, Emery Dreifuss), and channelopathies. Often inherited etiologies present in early childhood, but milder presentations occur later in adolescence or adulthood, thus making discerning the etiology of the myopathy challenging. 1,2

Some diagnostic clues include proximal or distal muscle involvement which can often be discerned by testing lumbopelvic strength with tasks such as rising from a chair, climbing steps, and sit-ups.3 Rashes, fevers/chills, and weight loss can help screen for systemic etiologies such as inflammatory, infectious, endocrine, and paraneoplastic sources. Initial laboratory evaluation might include CBC with differential, CK, LDH, BMP, AST/ALT, CRP, ESR, TSH, FT4, 25-OHD.3 Additional autoimmune testing that might be considered in the proper clinical context include ANA, Rheumatoid Factor, anti-dsDNA, anti-SSA, anti-SSB, anti-RNP, and a myositis antibody panel. MRI of the affected region can confirm myopathy, and muscle biopsy can often assist in the diagnosis.4 Maintaining a broad differential and screening for constitutional symptoms or atypical exam findings can assist in differentiating a myopathy from "growing pains" in the pediatric and adolescent population.

Editor's Comments:
As shown by the author’s team, patience with pediatric patients is crucial in diagnosis of neuromuscular or inherited inborn errors of metabolism disorders. Key factors to suspect this insidious condition are the progressive proximal weakness and pain. Muscular dystrophies are often most likely to present from late childhood into early adulthood. Along with progressive weakness, elevated creatine kinase levels can be an especially helpful tool in diagnosis of muscular dystrophies. 5

References:
1. Nagy H, Veerapaneni KD. Myopathy. Stat Pearls. 2023 Aug.
2. LePelusa A, Kentris M. Muscular Dystrophy. Stat Pearls. 2024 Jan.
3. Junnila JL, Cartwright VW. Chronic musculoskeletal pain in children: part I. Initial evaluation. Am Fam Physician. 2006 Jul 1;74(1):115-22.
4. Mammen AL. Autoimmune Myopathies. Continuum. 2016 Dec;22(6, Muscle and Neuromuscular Junction Disorders):1852-1870.
5. Saguil A. Evaluation of the Patient with Muscle Weakness. Am Fam Physician. 2005;71(7):1327-1336

Return To The Case Studies List.