Elevated levels of smooth muscle autoantibodies in patients with acromegaly

Screening of sera from patients with central nervous system (CNS) tumors for serum antibodies to tumor and normal tissue antigens revealed that the sera from a significant percentage of patients with pituitary adenoma demonstrated reactivity for smooth muscle antibodies (SMA) at a serum titer (1/25) at which other CNS tumors are devoid of this reaction. The sera were assessed by an indirect immunofluorescent antibody assay on fresh cryostat sections of rat kidney, liver, diaphragm, and stomach tissue. Absorption of SMA-positive sera with extracts containing smooth muscle tissue abolished the reaction. The overall incidence of SMA among patients harboring pituitary tumors was 30% (12/40). Assessment of the functional types of the tumor revealed a distinct predilection for such findings among patients with clinical acromegaly. Among patients with hypersecretion of growth hormone (CA) 90% (9/10) have SMA (both IgG and IgM type) whereas SMA was positive in only 10% (3/30) of corresponding group of patients with pituitary tumors resulting in hypercortisolemia or those that did not result in a hyperfunctional endocrine state.