Late-onset primary muscle diseases mimicking sarcopenia.

Sarcopenia is an age-related loss of skeletal muscle mass, strength, and function that causes various health problems. In contrast, late-onset primary myopathies, which occur in the older population, are caused by a variety of factors, including genetic mutations, autoimmune processes, and metabolic abnormalities. Although sarcopenia and primary myopathy are two distinct disease processes, their symptoms can overlap, making differentiation challenging. The diagnostic criteria for sarcopenia have evolved over time, and various criteria have been proposed by expert groups. Late-onset primary muscle diseases such as inclusion body myositis, sporadic late-onset nemaline myopathy, muscular dystrophies, distal myopathies, myofibrillar myopathies, metabolic myopathies, and mitochondrial myopathies share common pathogenic mechanisms with sarcopenia, further complicating the diagnostic process. Appropriate clinical evaluation, including detailed history-taking, physical examination, and diagnostic testing, is essential for accurate diagnosis and management. Treatment approaches, including exercise, nutritional support, and disease-specific therapies, must be tailored to the characteristics of each disease. Despite these differences, sarcopenia and primary myopathies require careful consideration in the clinical setting for proper diagnosis and management. This review outlines the evolution of diagnostic criteria and diagnostic items for sarcopenia, late-onset primary myopathies that should be differentiated from sarcopenia, common pathomechanisms, and diagnostic algorithms to properly differentiate primary myopathies. Geriatr Gerontol Int 2024; 24: 1099-1110.