Diffuse cutaneous systemic sclerosis is characterised by:
**Core Concept**
Diffuse cutaneous systemic sclerosis (dcSSc) is a subtype of systemic sclerosis (scleroderma) characterized by widespread skin thickening and fibrosis, often accompanied by significant internal organ involvement. This condition is associated with an autoimmune response and abnormal fibroblast activation.
**Why the Correct Answer is Right**
dcSSc is characterized by diffuse skin thickening and fibrosis, often involving the face, hands, and trunk. The condition is associated with the presence of autoantibodies, particularly anti-Scl-70 (also known as anti-topoisomerase I) antibodies, which are highly specific for dcSSc. The pathophysiology of dcSSc involves the activation of fibroblasts, which produce excessive amounts of collagen and other extracellular matrix proteins, leading to skin and internal organ fibrosis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because localized scleroderma, such as morphea, is characterized by localized skin thickening and fibrosis, without significant internal organ involvement.
**Option B:** This option is incorrect because limited cutaneous systemic sclerosis (lcSSc) is characterized by limited skin thickening and fibrosis, often sparing the face and trunk.
**Option C:** This option is incorrect because mixed connective tissue disease (MCTD) is a distinct autoimmune disorder that shares features of systemic sclerosis, lupus, and polymyositis, but is not characterized by diffuse skin thickening and fibrosis typical of dcSSc.
**Clinical Pearl / High-Yield Fact**
It's essential to distinguish between dcSSc and lcSSc, as the prognosis and treatment approach differ significantly between the two conditions. dcSSc often requires aggressive immunosuppressive therapy to prevent internal organ involvement and fibrosis.
**Correct Answer:** C. Diffuse cutaneous systemic sclerosis is characterized by diffuse skin thickening and fibrosis, often accompanied by significant internal organ involvement.