FIGURE 3
Coronal T1 weighted magnetic resonance imaging showing resolving mass within the right sternocleidomastoid muscle.
such as ischemia, vasculitis, and chromosomal abnormalities have also been suggested. 3
Proliferative myositis tends to affect individuals between the ages of 40 and 70 years, with occurrences in pediatric cases being extremely uncommon. 4 To our knowledge, this is the youngest case ever reported with the youngest case previously stated in the literature being 2.5 months old. 2 Radiologic studies will show a well-defined mass within a muscle belly without evidence of infiltrative or surrounding inflammatory changes. Biopsy can help exclude more concerning pathology such as a sarcoma. Histopathological examinations of proliferative myositis reveal cells that consistently stain positive for vimentin and actin, with a negative myoglobin stain. This staining profile implies a myofibroblastic lineage rather than a rhabdomyoblastic lineage. 4 The optimal approach to treating proliferative myositis is observation, as the majority of cases resolve spontaneously within one year. 3
CONCLUSION
Our case of potentially the youngest reported patient with this diagnosis underscores the importance of considering proliferative myositis in the differential diagnosis of rapidly growing neck masses in pediatric patients particularly when there is obvious muscular involvement. This condition must be differentiated from torticollis as proliferative myositis presents as a distinct mass with no limitations of neck range of motion. The combination of clinical evaluation, radiological imaging, and histopathological analysis is imperative to distinguish proliferative myositis from neoplastic or malignant entities, such as soft tissue sarcomas. Understanding the natural history of this condition helps avoid unnecessary surgeries, ensuring the patient receives the most appropriate care.
REFERENCES
1. Colombo JR, Dagher W, Wein RO. Benign proliferative myositis of the sternohyoid muscle: review and case report. Am J Otolaryngol. 2015; 36( 1): 87-89. doi: 10.1016 / j. amjoto. 2014.08.013
2. Meis JM, Enzinger FM. Proliferative fasciitis and myositis of childhood. Am J Surg Pathol. 1992; 16( 4): 364-372.
3. Shi J, Lewis M, Walsworth MK, Modaressi S, Masih S, Chow K Proliferative myositis Appl Radiol. 2018; 47( 1): 43-45.
4. Kent MS, Flieder DB, Port JL, Altorki NK. Proliferative myositis: a rare pseudosarcoma of the chest wall. Ann Thorac Surg. 2002; 73( 4): 1296-1298.
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West Virginia Medical Journal • June 2025 • 21