## 2 Case Presentation  
A 59-year-old man was transferred to the Padua University Hospital Haematology section for a fever of unknown origin and mild cytopenia. The patient had developed a mild fever and arthralgias two months prior to his presentation and was initially treated with Levofloxacin and steroids. The man was a social health care worker, and his medical history was notable for BRAF V600E mutated HCL [3; 4], diagnosed in 2018 and never treated. He had no history of vaccination with the Bacillus Calmette-Guerin. On April 2020 he was diagnosed with severe SARS-CoV2 disease that required mechanical ventilation and prolonged high-dose corticosteroids. His clinical course infection was also complicated by invasive fungal infection and deep vein thrombosis. During the hospitalization related to the SARS-CoV2 infection, a QuantiFeron-TB Gold test was performed and resulted negative. In the months following the SARS-CoV2 infection, the patient suffered from recurrent para-infective arthritis, which was treated with a long-term low-dose steroid therapy. On admission, his physical exam showed mild hepatomegaly and no evidence of ascites, jaundice or cutaneous erythematosus rash. Blood tests were notable for bilinear cytopenia (WBC 1.26 \(\times\) 10\({}^{9}\)/L, Neutrophphils 0.9 \(\times\) 10\({}^{9}\)/L, Monocytes 0.01 \(\times\) 10\({}^{9}\)/L, Hemoglobin 90 g/L, Platelets 134 \(\times\) 10\({}^{9}\)/L) and slight liver enzyme elevation (AST 71 U/L, n.v. 10-45 U/L; ALT 104 U/L n.v. 10-50 U/L), high C-reactive protein levels (150 mg/L, n.v. 0-6 mg/L) and procalcitonin levels (1.48 ug/L). Nasopharyngeal swab tested negative for SARS-CoV2. A CT scan revealed small lymph nodes (max \(\O\) 2 cm), ground-glass opacities in the lung parenchyma, splenomegaly (\(\O\) 19 cm), pleural and abdominal effusion (Supplementary Figure S1). The patient was then treated with broad-spectrum antibiotics, antipsychotics and high dose corticosteroids. Unfortunately, his clinical conditions failed to improve, as he developed spleen enlargement and his cytopenia progressively worsened. Subsequent blood tests showed an increase in the IL-2 soluble receptor (44.270 kW/L, n.v. 223-710 kW/L), elevated ferritin levels (39.286 ug/L, n.v. 31-409 ug/L) with a decrease in its glycosylated fraction (12%, n.v. 50-80%) and a further increase in liver enzyme levels (Figure 1). A diagnosis of HLH was made, as the patient fulfilled 6 out of the 8 HLH-2004 criteria [5], and the search for triggering factors was started. Blood, urine and sputum cultures were negative for most common bacteria and fungi. Galactomannan, \(\beta\)-D-glucan and serological tests were negative (including serologies for HIV 1 and 2, hepatitis C and hepatitis B), as well as tests for anti-nucleus antibodies and rheumatoid factor. A trephine bone marrow biopsy confirmed the HCL diagnosis and excluded histological transformation to a high-grade B-cell lymphoma or T-cell non-Hodgkin lymphoma. The patient's condition started to worsen rapidly, and he required transfer to the intensive care unit for vasopressor support and mechanical ventilation. At this time, a QuantiFeron-TB Gold test became \"indeterminate-positive\", and prolonged blood culture (sample collected near the date of the patient's admission, result obtained two months after collection) revealed a _Mycobacterium tuberculosis_ complex (MTC) [6]. Cultures of the pleural effusion were negative, also for MTC. The presence of active neoplasia and positive blood culture ruled out the diagnosis of Adult-Onset Still's Disease [7], and the patient was diagnosed with sHLH syndrome due to disseminated tuberculosis [8]. The man was initially treated with steroids, etoposide and rituximab to switch off the cytokine storm released by macrophages, with mild improvement, and subsequently with anti-MTC therapy (isoniazid 150 mg twice daily, rifampicin 300 mg twice daily, ethambutol 1200 mg daily, pyrazinamide 500 mg daily.