The correct answer is C. IgA.

IgA. The rash in the picture is consistent with Sneddon-Wilkinson or subcorneal pustular dermatosis. Some patients with Sneddon–Wilkinson disease have an associated IgA paraproteinemia.

Scleromyxedema is associated with IgG lambda gammopathy. Necrobiotic xanthogranuloma can be associated with IgG (usually kappa) paraproteinemia. Schnitzler syndrome is a chronic urticaria associated with monoclonal gammopathy. Typically, an IgM gammopathy is found (mainly kappa).

References:

1. Bolognia JL, Schaffer JV, Cerroni L, Callen JP. Dermatology Volume 2. Edinburgh Elsevier; 2018.
2. Elston DM. Dermatopathology. Elsevier; 2019.

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