Inclusion body myositis. Genetics, biomarkers and muscle biopsy

Sporadic inclusion body myositis is the most common idiopathic inflammatory myopathy over the age of 50, with a male-to-female ratio of 3:1. Symptoms onset before age of 60 occurs in 18-20% of patients, with a delay in diagnosis of 5 to 8 years.The classic clinical presentation of SIBM consists of proximal leg and distal arm weakness, and most commonly patients present early slowly progressive quadriceps weakness which leads to falls and to difficulties in climbing stairs, while less common the initial complaints refer to finger flexor weakness and atrophy, foot drop, or dysphagia, and rare presentations include prominent forearm weakness, sparing the quadriceps. The aetiopathogenesis of the disease remains unclear and despite some preliminary promising results, to the day there is no effective treatment.The diagnosis of SIBM is based on the clinical presentation and the histopathological findings in muscle biopsy, however increasing evidence on genetics and paraclinical biomarkers has recently come to light giving new insights on the pathogenesis, the diagnosis and the potential treatment of the disease. In the present study we aim to review the histopathological findings, genetics and blood biomarkers, and to review the role of muscle biopsy in the diagnosis of SIBM.