Focal Myositis Diagnosed Using Point-of-Care Ultrasound (POCUS): A Case Report
Dr Himanshu Gul Mirani
Case Presentation:
A 38-year-old male with no significant medical history presented to the Emergency Department (ED) with progressive swelling and redness of the left elbow. Three days earlier, he had accidentally hit his elbow against a car door. There was no associated fever or systemic symptoms.
On examination, the left elbow was swollen and erythematous, with warmth over the affected area. The patient retained full range of motion in the elbow joint, with no significant pain during flexion or extension. Differential diagnoses included septic arthritis and olecranon bursitis.
Point-of-care ultrasound (POCUS) was utilized to evaluate the swelling. It ruled out joint effusion and olecranon bursitis. Instead, an irregular hypoechoic area was visualized within the hyperechoic muscle, consistent with focal myositis. Surrounding cellulitic changes were noted, characterized by the typical cobblestone appearance.
Laboratory results included:
• Haemoglobin: 149 g/L
• White cell count: 15.4 × 109/L (neutrophils: 12.25 × 109/L)
• Platelets: 196 × 109/L
• C-reactive protein (CRP): 115 mg/L (normal <5 mg/L)
• Creatine kinase: Normal
Longitudinal section
Management and Outcome:
The patient was started on intravenous antibiotics. With improvement in inflammatory markers, he was transitioned to a two-week course of oral antibiotics. His symptoms resolved without complications, and no additional imaging was required.
Focal myositis is a rare, localized inflammatory myopathy often misdiagnosed as other soft tissue conditions, including abscesses, septic arthritis, or bursitis. While the etiology remains unclear, it is frequently idiopathic and self-limiting. A major diagnostic pitfall is the absence of elevated creatine kinase (CK) levels, a common feature in other myopathies.
Imaging is essential for accurate diagnosis. POCUS, in particular, plays a critical role in distinguishing focal myositis from abscesses and other inflammatory conditions, facilitating appropriate management. In this case, POCUS provided clarity by identifying hypoechoic changes within the muscle while ruling out other potential diagnoses, thus avoiding unnecessary interventions.
Key Learnings and Points:
Published literature underscores the importance of imaging in focal myositis. For example,
Yousef et al. (2022) reviewed 32 cases and found that CK levels were normal in 60% of
patients, highlighting the limitations of relying solely on laboratory tests. Similarly, Műller et al.
(2021) emphasized the role of ultrasound and MRI in differentiating focal myositis from neoplastic or infectious conditions. These findings align with the present case, which demonstrates the utility of POCUS in the ED setting.
This case highlights the diagnostic value of POCUS in rare conditions like focal myositis. Its ability to rule out abscesses and bursitis ensures timely and appropriate management. Clinicians should maintain a high index of suspicion for focal myositis, even with normal CK levels, and utilize imaging tools to confirm the diagnosis.