Mycobacterium Avium Complex (MAC) are a group of mycobacteria, which are found widely in the environment such as in soil and drinking water and are generally not harmful to the majority of healthy people  . They occasionally cause respiratory infections, or more fulminant infections in immunosuppressed individuals  . The US Food and Drug Administration (FDA) have recently issued an alert relating to the association of non-tuberculous mycobacterial infections such as MAC with heater-cooler devices primarily used in cardiothoracic surgical procedures  . The majority of cases have been prosthetic heart valves that have become infected either through contaminated water entering the devices or aerosolised bacteria transmitted through exhaust vents  . In some cases, patients presented with infections several months to years after their surgical procedure   .
Hemophagocytic lymphohistiocytosis (HLH) is a frequently fatal and underdiagnosed disease involving a final common pathway of hypercytokinemia, which can result in end-organ damage and death  . Secondary HLH presents with a systemic inflammatory response syndrome (SIRS) and diagnosis requires five of the following eight criteria to be met; 1) fever, 2) cytopenia of two lines, 3) hypertriglyceridemia and/or hypofibrin-ogenemia, 4) hyperferritinemia (>500 microg/L), 5) hemophagocytosis, 6) elevated soluble interleukin-2 receptor (CD25), 7) decreased natural killer-cell activity, and 8) splenomegaly. There have been case reports confirming links between HLH and disseminated MAC or secondary to Mycobacterium tuberculous, however no documented case with M. chimaera  . Typical patient presentation involves unexplained fevers, weight loss and pancytopenia. We present a case of HLH secondary to M. chimaera infection of a prosthetic heart valve.
2. Case Presentation
2.1. Case History
A 72-year-old Caucasian gentleman was admitted to hospital with a progressive pancytopenia and a one-month history of unintentional weight loss and fevers (temperature >38˚). The patient had a past medical history of a prosthetic aortic valve replacement (AVR) for critical aortic stenosis in 2014. On clinical examination there was no stigmata of endocarditis with normal heart sounds however a spleen was palpable (Table 1).
A transoesophageal echocardiogram revealed an intact tissue aortic valve with normal flow and no visible vegetations. Full blood count revealed pancytopenia (Hb 89 g/L, WBC 1.87 × 109/L, plts 69 × 109/L) and peripheral blood film showed red cell anisopoikilocytosis, acanthocytes and pencil cells with a negative haemolysis screen and mildly abnormal haematinics (Vitamin B12 337 pg/mL, folate 2.8 ng/mL, iron 8.0 mcg/dL).
In view of pancytopenia and splenomegaly, HLH was suspected and further biochemistry results showed an elevated ferritin 1677 ng/ml and triglyceride of 2.1 mg/dL. A bone marrow biopsy was performed, demonstrating the presence of numerous phagocytosing histiocytes suspicious of macrophage activation and non-necrotic microgra-
Table 1. Patient demographics.
Radiological imaging only revealed mild splenomegaly with no occult malignancy and virology testing including Hepatitis B, C and HIV was negative. Microbiology investigations with serial peripheral blood cultures performed persistently isolated Mycobacterium Intracellulare, later confirmed to be M. chimaera.
2.3. Management and Case Progression
To combat the Mycobacterium infection, the patient was commenced on a prolonged course of combination of antibiotics including Clarithromycin, Rifampicin, Ethambutol and Amikacin. Intravenous Immunoglobulin (IVIg) was given weekly to inhibit haemophagocytosis, resulting in improvement in pancytopenia, hyperferritinaemia (Figure 2) and constitutional symptoms.
Table 2. 2004 HLH diagnostic criteria  .
Figure 1.Bone marrow trephine specimen showing; (a) numerous histiocytes packed with red blood cells (circled) ×40 lens (b) microgranuloma and phagocytosis of erythrocytes (circled) × 100 lens.
Figure 2. Demonstration of pancytopenia with subsequent improvement following IVIg and antibiotics.
Despite the initial improvement in blood counts, the patient has remained moderately pancytopenic following one year follow up with recurrent septic episodes and is currently being managed palliatively.
HLH is a potentially fatal condition in which abnormal activation of the immune system results in haemophagocytosis, inﬂammation and tissue damage  . The underlying pathophysiology is not fully understood but involves an abnormal activation of the immune system, including macrophages, Natural Killer (NK) cells and cytotoxic lymphocytes   . In particular, there is failure of normal auto-regulation of NK cell function, increased activation and proliferation of lymphocytes and macrophages, and increased production of cytokines, which ultimately results in uncontrolled haemophagocytosis   .
Secondary HLH can occur in association with infections, most commonly viral infections, but has also been associated with fungal, parasitic and bacterial infections, including Mycobacterium species. Prompt identification of the underlying cause of HLH is important as it guides treatment decisions and early initiation of appropriate treatment reduces morbidity and mortality. Current treatment of primary HLH follows the HLH-2004 treatment protocol, which can also be beneﬁcial for patients with secondary HLH  and consists of a combination of chemo-immunotherapy agents. However, in cases of secondary HLH in association with non-viral infections, targeted treatment involves anti-microbial and IVIg therapy  .
Acquired HLH can pose a clinical conundrum for clinicians and rigorous investigation into past medical and surgical history can allude to the cause. Although Mycobacterium is a well-documented precipitant of haemophagocytosis, this is the first case documented in the literature with M. chimaera precipitated by an infected prosthetic valve. Prolonged broad-spectrum antibiotic therapy as well as IVIg can arrest the progression of HLH and improve pancytopenia.