Abstract Background and Aims Diffuse alveolar haemorrhage (DAH) is a serious manifestation of diseases such as systemic lupus erythematosus (SLE) and, apparently in a paradoxical manner, antiphospholipid syndrome (APS). Inflammation resulting from the deposition of immune complexes in alveolar capillaries appears to contribute to the pathophysiology of DAH, SLE and APS. Symptoms include cough, dyspnoea, haemoptysis or fever. It is associated with a drop in haemoglobin, respiratory failure and diffuse infiltrates on imaging exams. Bronchoscopy is diagnostic. It is important to exclude infection as treatment includes high-dose corticosteroid therapy and other immunosuppressive drugs. We present a challenging case regarding the diagnostic and therapeutic approach to this pathology. Case report This is the case of a 52-year-old Caucasian female, with a history of SLE, APS, splenectomy due to thrombocytopenia, IgM Kappa monoclonal gammopathy and indolent non-Hodgkin lymphoma. She was medicated with prednisolone 5 mg and warfarin (target INR between 2 and 3). The patient was observed due to a 1-day history of fever, nasal obstruction and odynophagia, associated with progressively worsening fatigue. On examination, she was pale, eupnoeic, tachycardic, with bibasal rales and a hyperaemic oropharynx. Lab workup results were the following: haemoglobin 7 g/dL (11.7 g/dL 3 months before), VGM 71 fL, presence of schistocytes, leukocytes 13.7 G/L, neutrophils 11.1 G/L, PCR 4.6 mg/dL, platelets 170 G/L, INR 3.6, aPTT 45 sec, negative D-Dimers, urea 54 mg/dL, creatinine 1.4 mg/dL, LDH 431 IU/L, normal haptoglobin, negative Coombs test. In arterial blood gas analysis, pO2 was 61 mmHg and lactate was 5 mmol/L. Chest X-ray showed bilateral basal cotton-wool infiltrates and chest CT showed bilateral ground-glass pattern. The rest of the investigation included no complement consumption, negative anti-ds-DNA antibody, positive lupus anticoagulant, anticardiolipin and anti-beta2-glycoprotein antibodies, negative cryoglobulins and no evidence of progression of the lymphoproliferative disease. She was admitted to the intensive care unit due to suspicion of atypical/viral pneumonia vs. DAH. Oxygen therapy, empirical antibiotic therapy with ceftriaxone and clarithromycin and oral methylprednisolone 1 mg/Kg/day were started. She needed blood transfusion, although without visible blood loss. Bronchofibroscopy was performed, with bronchoalveolar lavage suggestive of DAH, so it was decided to start intravenous pulses of methylprednisolone, plasmapheresis, and intravenous immunoglobulin (IVIG). Warfarin was changed to unfractionated heparin. The patient had clinical, analytical and radiological improvement. Due to the lack of evidence of infection, antibiotics were stopped after 7 days. The patient was discharged under weaning corticosteroid therapy and monthly IVIG (during 5 months), without recurrence in the following year. Conclusion This is a rare case of oligosymptomatic DAH in a patient with SLE and APS. The literature currently available on DAH in the context of SLE or APS is scarce and its treatment is mainly dependent on the experience of each medical centre. Corticosteroid therapy is consensual, with greater variability in other corticosteroid-sparing therapies. In the case of patients with APS, anticoagulation is a challenge, and it is important to resume it as soon as the bleeding is controlled due to the risk of thrombotic events.