hemophagocytic lymphohistiocytosis ( hlh ) secondary to infectious disease is an important entity especially in tropics where infectious diseases are rampant and still pose a major threat . a timely diagnosis and prompt treatment can improve the clinical outcome of this otherwise potentially fatal condition ! this article aims to alert the clinicians that in persistent unresolved fever especially in tropics , a diagnosis of secondary hlh should be given due consideration and we present 6 cases in this paper . all patients presented between march 2012 and march 2013 ( details shown in table 1 ) and fulfilled the revised criteria of hlh as listed in table 2 . of them , the mean age at diagnosis was 33.83 years ( range : 20 to 64 years ) , with a male : female ratio of 2:1 . three patients presented with evidence of hepatomegaly and/or splenomegaly . all of the patients had at least a bi- or trilineage cytopenia , elevated liver enzymes and hyperferritinemia . two of the cases were secondary to dengue fever and one secondary to disseminated tuberculosis , one secondary to pulmonary tuberculosis , one secondary to malaria ( falciparum ) and one secondary to leptospirosis . all patients had good recovery and none of them relapsed at a median follow up of 4 months . characteristics of secondary hlh patients m  male ; f  female , y  yes ; n  no ; csa  cyclosporine ; na  not available proposed hlh diagnostic criteria , 2009 ravenous macrophage - hemophagocytosis of rbcs by macrophage seen hlh is a hyper - inflammatory condition which may be familial or occur secondary to autoimmune diseases or infection , malignancy or other triggers . despite advances in the diagnostic work up of febrile patients , hlh remains elusive from the diagnostic capabilities of many clinicians and continues to be a potentially fatal disease entity . the underlying pathophysiology of the disease constitutes an unrestrained immune activation with defective macrophage function regulation . an excessive activation of macrophages leads to a cytokine storm in the host and leads to host tissue damage and organ dysfunction associated with the syndrome . excessive pro - inflammatory or defective anti - inflammatory responses leading to this cytokine storm can be triggered by host factors or environmental agents . accordingly , a hlh arising in the setting of an underlying genetic mutation is termed familial hlh , in the setting of an underlying rheumatologic disease like rheumatoid arthritis is termed as macrophage activation syndrome ( mas ) and in the setting of an underlying infection it is termed as reactive or secondary hemophagocytic syndrome ( hps ) or secondary hlh . case reports describing mas post bone marrow transplant in patients with juvenile rheumatoid arthritis , or secondary to sle or dermatomyositis or other autoimmune diseases have been reported . macrophage and neutrophil activation is a hallmark in conditions like stills disease which can lead to hyperinflammatory condition with hlh . overproduction of proinflammatory cytokines , uncontrolled activation of t cells , and macrophages associated with decreased natural killer cell and cytotoxic cell functions seem to be the hallmarks of the immunologic abnormalities in mas . recent human and murine investigations suggest that all hpss should be differentiated based on etiology and pathogenesis as treatment strategies for each may vary . however , all etiologies lead to a state of hyper ferritin levels . the precise mechanism of ferritin as a trigger or a bystander in pathogenesis needs to be explored . the reactive or infection - associated hlh remains a relatively important and yet unfortunately an underdiagnosed entity especially in the tropical world . various combinations of high grade fever sometimes a second spike of fever after a brief period of recovery which coincides with fresh cytopenias , unresponsiveness to broad - spectrum antibiotics , new onset organomegaly or sudden increase in size of organomegaly in the setting of an infectious disease are some of the diagnostic clues for this disease . in case of infections , a simple blood investigation that shows elevated levels of serum ferritin should raise the suspicion of a coexisting hlh . a tentative diagnosis of hlh for initiation of immunosuppressive therapy can be done when clinical and lab abnormalities exist as defined in revised 2009 hlh protocol . also , in the resource poor settings , a single value of ferritin more than 10,000 in the absence of iron overload conditions like hemochromatosis and thalassemia syndromes can act as a surrogate marker for hlh with a sensitivity of 90% and specificity of 96% . hps secondary to infections has been classified as a separate entity under international classification of diseases by world health organization . other viruses like dengue , herpes , cmv , hiv have been reported to have hps secondary to them . secondary hps has frequently been associated with intracellular pathogens that stimulate th1 immune response . of the bacterial infections , other reports with organisms like salmonella , leptospirosis , malaria , toxoplasmosis , leishmenia , rickettsia and other organisms have been postulated in secondary hlh . although case reports and case series have frequently reported the reactive hlh secondary to infectious causes especially in the tropical countries , it continues to remain as an under diagnosed and under - reported entity . the treatment of secondary hlh includes aggressive treatment of underlying condition along with immunosuppressive therapy . however , recent data suggest to a less intense immunosuppressive therapy . as opposed to the familial hlh , where allogenic stem cell transplant is the only curative treatment , most of the infection associated hlh cases respond to a course of corticosteroids . some patients may need additional treatment with drugs like etoposide and cyclosporine ; however , a full course of hlh 2004 protocol is rarely required in them . in our case series , all patients were initiated with dexamethasone at a dose of 10 mg / m / day . three patients with hlh secondary to underlying tuberculosis , malaria and leptospirosis [ case 2 , 5 , 6 in table 1 ] each responded to steroid monotherapy . within 2 days of starting steroids their fever reduced with improvement in cytopenias . one patient with dengue fever had a ferritin values more than 100,000 along with severe pancytopenia . she was given two doses of etoposide iv at a dose of 100 mg / m ( reduced dose ) at weekly intervals . other two patients were given one single dose of etoposide following which they became symptomatically better . one patient with dengue and one with tuberculosis however had delayed recovery of platelet count and they were started on oral cyclosporine . csa was given for duration of three months following which it was tapered and stopped . this is in tune with the other case reports and case series of secondary hlh . one possible explanation for this is removal of inciting agent by means of effective antibacterial therapy . because of its powerful proapoptotic activity describe their unique experience with stem cell transplant in treating secondary hlh in an adolescent . srinivas et al . in their systemic review of hemophagocytosis syndrome ( hps ) in tropics found infectious trigger as the cause in 51% of the adult patients . leishmenia was seen in 40.6% , rickettsia in 18.8% malaria in 15.6% and enteric fever in 9.4% . 56% patients were secondary to viruses , 26% secondary to dengue virus , 17.3% were secondary to ebv and 8.7% each to cmv and parvovirus b 19 . most of the literature on hlh in tropics is centered on few hospitals and includes case reports and case series . larger studies and trials are required to throw more light on this potentially fatal condition and unfold the mysteries of ravenous macrophages . in india , hlh associated with dengue fever and malaria with a high parasite index has been documented . in one study from india , the dengue virus has been found to be the most common agent causing hlh in children . many of the previous case reports of hlh are reported in complicated dengue fever like dengue hemorrhagic syndrome . crohn 's disease and immunosuppression are associated with an increased risk for developing secondary hlh , although none of our patients had underlying disease or immunosuppressed status .. however , cases with classical dengue syndrome have also been reported from indian subcontinent . in our series also , we report two cases of classical dengue fever with secondary hlh . our cases add to the existing literature of handful of cases of hlh in dengue . although more common in tropics a case of elderly female has been described by cdc , usa in which hlh secondary to possible dengue infection proved fatal and physicians in west need to be alerted about possible travel acquired dengue which can have fatal complications like secondary hlh . describe the time - lines of six cases of confirmed dengue with varying severities of hemophagocytosis . both our patients presented with fever , pancytopenia , organomegaly , high ferritin and fulfilled the criteria of hlh and responded to corticosteroids and etoposide . hlh secondary to malaria was reported in a young man ( case number 5 ) who had persistent fever , falling counts despite treatment with antimalarials . had described one of the first cases of hemophagocytosis secondary to malaria ( falciparum ) which resolved with antimalarials . park et al . discusses four case reports of hlh secondary to vivax malaria all of which resolved with antimalarials . however , studies in the pediatric population show degree of parasitemia is associated with severity of disease . similarly our case was secondary to p falciparum malaria with severe parasitemia seen on peripheral smear . the patient responded to corticosteroids .. hlh secondary to disseminated tuberculosis has been described in past . pristilla et al . in their review analyzed 36 cases of tuberculosis with secondary hlh . they found fever to be the most common presenting symptom and evidence of extra - pulmonary tuberculosis was found in 83% of cases . in our series , case number 2 a young boy with fever , weight loss , military tuberculosis and choroid tubercles was diagnosed as a case of disseminated tuberculosis . no significant improvement with anti tubercular treatment prompted us to look for other causes and was diagnosed as secondary hlh based on clinical features , high ferritin and bone marrow evidence of hemophagocytosis . steroids were added to his treatment course and he showed significant improvement within 2 weeks . similarly an elderly female was diagnosed to have hlh secondary to pulmonary tuberculosis and was started on steroids . however , she did not improve and was further treated with iv etoposide and oral cyclosporine and showed complete remission of symptoms and evidence of hemophagocytosis on follow up after 4 week . this is consistent with earlier studies which showed negative tuberculin test should never preclude the possibility of overwhelming tubercular infection in hlh . leptospirosis is a spirochete which is commonly prevalent in coastal belt of south india . to the best of our knowledge , no case of hlh secondary to this disease in adult has been reported . the diagnostic challenge in making appropriate diagnosis has been discussed in one of the previous case reports from taiwan in a young male who presented with shock and had evidence of reactive hemophagocytosis . our patient was a fisherman from the endemic area who presented with fever and oliguria . in due course he developed hepatosplenomegaly , severe cytopenia , esr of 5 , high ferritin and bone marrow evidence of hemophagocytosis . in conclusion with limited experience and lack of guidelines for treatment of tropical hlh , a high index of suspicion is something clinicians should bear in mind .
hemophagocytic lymphohistiocytosis ( hlh ) is a potentially fatal hyper inflammatory condition , if not recognized and treated in time . 
 a high index of suspicion can help identify the condition early . 
 this condition can occur in the primary or secondary form . 
 secondary hlh or hemophagocytic syndrome ( hps ) secondary to infections is an important clinical entity especially in tropical world . in this article 
 , we share our experience with this entity and make an attempt to explore literature about ravenous macrophages which occurs secondary to infections . 
 it is a series of six cases of hlh secondary to infectious disease in our center in a coastal city in south india over last one year with follow up .