Limb girdle muscular dystrophy type 2B masquerading as inflammatory myopathy: case report

Area of Science:

• Neurology
• Genetics
• Musculoskeletal Disorders

Background:

• Limb girdle muscular dystrophy type 2B (LGMD2B) is a rare genetic myopathy characterized by muscle weakness.
• It results from dysferlin gene mutations, leading to reduced or absent muscle dysferlin.
• LGMD2B can present with symptoms that overlap with inflammatory myopathies.

Purpose of the Study:

• To report a case of LGMD2B presenting with significant knee pain and swelling.
• To highlight the diagnostic challenges due to symptom mimicry of inflammatory myositis.
• To emphasize the importance of considering non-inflammatory causes in cases of unexplained pain.

Main Methods:

• Case report of a 10-year-old boy with severe knee pain and elevated creatine kinase.
• Diagnostic workup included blood tests (CK, CRP, ESR), MRI, and muscle biopsy.
• Genetic testing confirmed compound heterozygous pathogenic mutations in the dysferlin gene.

Main Results:

• The patient exhibited severe knee pain and swelling, initially unilateral then bilateral, with pain worsening at rest.
• Markedly elevated creatine kinase levels suggested inflammatory myositis, further supported by MRI findings.
• Muscle biopsy revealed significantly reduced dysferlin immunostaining, confirming LGMD2B.
• Normal CRP and ESR levels were noted despite pain suggestive of inflammation.

Conclusions:

• LGMD2B can present atypically with severe pain mimicking inflammatory myositis.
• A high index of suspicion is crucial for accurate diagnosis, especially when inflammatory markers are normal.
• Characteristic inflammatory-related morning pain should not exclude consideration of LGMD2B.