antiphospholipid syndrome ( aps ) is an autoimmune disease characterized by thrombosis and morbidity , specifically in pregnancy , due to antiphospholipid antibodies . about half of the cases of aps occur as a primary disorder , while the rest arise in association with other autoimmune diseases , such as systemic lupus erythematosus ( sle ) . some diseases , such as pulmonary thrombosis and pulmonary hypertension , are known to be complicated by aps ; however , aps with pleural effusion is extremely rare . here , we present a case of aps complicated by unilateral pleural effusion that responded well to oral corticosteroid therapy . a 75-year - old japanese man was admitted to our hospital for spreading erythema on his trunk and extremities , as well as dyspnea . one year prior to admission , he visited us with a 1-year history of erythema and purpura on his legs , accompanied by intermittent fever . results of laboratory examinations for antiphospholipid antibodies , lupus anticoagulant ( using the phospholipid neutralization test ) , and anticardiolipin antibody had been positive 12 weeks apart . in addition , he showed positive antinuclear antibody ( 1:80 , homogeneous pattern ) , but was negative for anti - dsdna antibody , anti - sm antibody , anti - rnp antibody , anti - ss - a antibody , anti - ss - b antibody , antitopoisomerase i antibody , and anticentromere antibody . mpo - anca , pr3-anca , and cryoglobulin were negative . given the diagnosis of aps , we initiated combination therapy with aspirin ( 100 mg daily ) and warfarin ( target international normalized ratio , 2.03.0 ) , but the skin lesions continued to gradually worsen . violaceous erythema , purpura , and pigmentation were widely noted on his trunk and extremities ( fig . 1 ) ; they were associated with low platelets ( 93,000/l ) and elevated partial thromboplastin time ( 48.4 s ) . a biopsy specimen revealed marked thrombosis in the dermal and subcutaneous small vessels ( fig . 2 ) . there were interface changes of the dermo - epidermal junction and mild inflammatory infiltrates in the perivascular area of the dermis , but mucin deposition and thickening of the basal layer of the epidermis were not apparent . in addition , a chest x - ray and computed tomography demonstrated a large pleural effusion in the left lung ( fig . 3 ) , without evidence of large vessel thrombus . electrocardiogram and echocardiogram were normal . despite serial thoracenteses , effusion recurred . bacterial and fungal cultures , as well as cytology analyses for malignant cells , were all negative . after excluding infectious diseases , malignancies , pulmonary thrombosis , and heart failure , we added oral prednisolone ( 30 mg daily ) to his prior anticoagulant regimen . the skin lesions and the pleural effusion improved rapidly , eventually disappearing without complication ( fig . 4 ) . on follow - up clinical examinations , no symptoms related to sle or other collagen diseases were noted . common causes of pleural effusion include malignancies , infectious diseases , pulmonary embolism , collagen vascular disease , and heart failure . aps - related pleural effusion has rarely been reported , and those cases that have been reported appeared to be complications of accompanying pulmonary embolism , sle , or catastrophic aps [ 4 , 5 , 6 ] . pleuritis , which can induce pleural effusion , is the most common pleuropulmonary manifestation of sle . in the present case , after excluding these differential diagnoses , aps was determined to be the direct cause of the pleural effusion . however , a strong possibility still exists that the pleural effusion may be associated with occult collagen vascular disease , particularly sle or lupus - like disease ( lld ) heretofore undiagnosed . a long - term follow - up study in 128 patients with primary aps demonstrated that 11 patients ( 8% ) developed sle , while 6 ( 5% ) developed lld during a median follow - up period of 8.2 years ( range , 114 years ) . the results of this study suggest that the pleural effusion may be attributed to a coexisting condition like lld , although our patient has not fulfilled american college of rheumatology diagnostic sle criteria to date . this may be supported by the fact that oral corticosteroid therapy was a remarkably effective treatment of the pleural effusion that had previously been unsuccessfully treated by anticoagulant therapy and repeated drainage . corticosteroids and immunosuppressants continue to be the treatment of choice for severe sle complications , including pleural effusion . furthermore , the clinical manifestations of primary aps and aps associated with sle are similar , which makes it more difficult to differentiate these diseases . as pleural effusion can be life - threatening corticosteroids might be an effective choice of treatment for intractable pleural effusion in aps patients .
antiphospholipid syndrome ( aps ) with pleural effusion is extremely rare . 
 a 75-year - old man was admitted to our hospital for spreading erythema on his trunk and extremities , as well as dyspnea . 
 one year before admission , he had visited us with a 1-year history of erythema and purpura on his legs and occasional fever . 
 given the diagnosis of aps , we initiated a combination therapy of aspirin and warfarin , but the skin lesions had gradually worsened . 
 a biopsy specimen revealed marked thrombosis in the dermal and subcutaneous small vessels . 
 in addition , chest x - ray and computed tomography demonstrated a large pleural effusion in the left lung . 
 he underwent repeated drainage of the pleural effusion but the effusion recurred . 
 we added oral prednisolone 30 mg daily to his prior anticoagulant therapy . 
 the skin lesions and pleural effusion rapidly improved and disappeared without any complication . 
 corticosteroids might be a choice of treatment for intractable pleural effusion in aps patients .