What condition might involve fibrous changes in the internal organs?

Progressive systemic sclerosis, also known as scleroderma, is characterized by the abnormal accumulation of collagen leading to fibrous changes in the skin and internal organs. This condition involves a cascade of pathological processes where fibrosis can develop within various organ systems, including the heart, lungs, kidneys, and gastrointestinal tract. As a result, individuals may experience a range of symptoms such as skin tightening, pulmonary hypertension, renal impairment, and difficulty with digestion.

The fibrotic changes are a direct consequence of the autoimmune nature of progressive systemic sclerosis, where the immune system erroneously attacks the body's own tissues, resulting in excessive collagen deposition and organ dysfunction. This distinguishes it from conditions like systemic lupus erythematosus, which primarily affects the skin, joints, and multiple organs but does not typically cause the level of fibrosis seen in scleroderma.

In other conditions mentioned, osteoarthritis primarily affects joints without causing systemic fibrotic changes, while fibromyalgia is characterized by widespread musculoskeletal pain without the fibrotic response or involvement of internal organs. Hence, progressive systemic sclerosis is the condition that directly correlates with fibrous changes in internal organs.