Macular amyloidosis. Macular and pigmented lesion on a patient's back. Macular amyloidosis is a condition where deposits of amyloid (a glycoprotein) accumulate in the skin. The macules may be itchy, but are otherwise harmless. The cause is unknown, but in some cases it is inherited and it is more prevalent in patients with darker skin. The itch can be treated with topical steroids or emollients.