This patient with glomerulonephritis, photosensitive skin rash, and arthralgia has systemic lupus erythematosus (SLE).  Many patients with SLE have circulating antiphospholipid antibodies (ie, lupus anticoagulant [LA], anticardiolipin antibody [aCL], anti-beta-2 glycoprotein I antibody).

Antiphospholipid antibodies interfere with common serologic tests: LA cross-reacts with phospholipid reagents in the activated PTT test, and aCL binds cardiolipin, the predominant antigen used in the rapid plasma reagin (RPR) and VDRL tests.  Therefore, patients with circulating antiphospholipid antibodies have paradoxical PTT prolongation and false-positive RPR/VDRL results.  Bleeding time and PT, which are coagulation tests unaffected by antiphospholipid antibodies, are normal.

Patients with antiphospholipid antibodies (with or without the concomitant diagnosis of SLE) are at risk for antiphospholipid antibody syndrome (APS), a hypercoagulable disorder characterized by venous (eg, deep vein thrombosis) or arterial (eg, ischemic stroke) thrombosis.  The presence of antiphospholipid antibodies promotes thromboembolism due to activation of phospholipid-dependent coagulation pathways.

Patients with APS have increased obstetric morbidity, including recurrent pregnancy loss, preterm delivery due to preeclampsia or placental insufficiency, and stillbirth.  The underlying mechanism is likely thrombosis of placental vessels, which decreases perfusion to the fetus.

(Choices A and B)  Hemophilias (eg, inherited deficiency of factor VIII, IX, or XI) can cause prolonged activated PTT but normal PT; these patients may have heavy menstrual bleeding and/or painful hemarthroses (bleeding into a joint).  However, in the setting of SLE, this patient's abnormal coagulation test results are more consistent with interference by antiphospholipid antibodies than an inherited coagulopathy.

(Choice D)  Sclerodactyly can occur with other autoimmune diseases such as scleroderma or CREST (Calcinosis cutis, Raynaud phenomenon, Esophageal dysmotility, Sclerodactyly, Telangiectasia) syndrome.  However, it is does not typically occur with SLE.

(Choice E)  Tabes dorsalis is a manifestation of tertiary syphilis that results in sensory ataxia.  Because this patient has a negative specific treponemal test (Treponema pallidum enzyme immunoassay [TP-EIA]), her positive RPR test result is likely a false-positive, and therefore she is not at risk for tabes dorsalis.

Educational objective:
Many patients with systemic lupus erythematosus have antiphospholipid antibodies, which can cause paradoxical PTT prolongation and false-positive RPR/VDRL results; antiphospholipid antibody syndrome is characterized by arterial or venous thrombosis and increased obstetric morbidity (eg, recurrent pregnancy loss).