In which condition is the patient typically unresponsive to steroids and has a chronic progressive course?

Inclusion body myositis (IBM) is characterized by a chronic, progressive muscle weakness and atrophy, typically affecting individuals over the age of 50. The hallmark of this condition is its resistance to steroid treatment. Unlike other inflammatory myopathies, such as dermatomyositis and polymyositis, which often respond favorably to corticosteroids, patients with IBM do not exhibit a significant improvement with this type of therapy.

Additionally, inclusion body myositis presents with specific clinical features, such as muscle weakness that predominantly affects the proximal and distal muscles in a gradual manner. This distinguishes it from conditions like myasthenia gravis, which is primarily a neuromuscular junction disorder and responds to different types of treatment such as acetylcholinesterase inhibitors and immunotherapy. The chronic nature of IBM, combined with the lack of response to steroids, makes it a unique entity within the spectrum of muscle disorders.