![]() 13, 46-50 Although most patients with underlying genetic defects show the features summarized in Table 4, cellular expression of perforin, SLAM-associated protein, X-linked inhibitor of apoptosis protein proteins, or CD107a (a glycoprotein necessary for degranulation of perforin-containing granules from cytotoxic lymphocytes) may be normal or nearly normal in rare cases. Genetic defects leading to FHL, with impairment of lymphocyte cytotoxicity, and genetic alterations in related disorders are presented in Table 4. ![]() 19, 21, 31-41 Other diagnostic toolsįunctional and genetic testing are not generally recommended in adult patients with HLH because abnormalities are rarely detected. Various case series have used modified HLH-2004 criteria. ![]() 29, 30 The HLH-2004 criteria, developed for children, are not validated formally for adults and remain based on expert opinion. 27, 28 Soluble interleukin-2 (IL-2) receptor (also soluble CD25 ), 1 of the diagnostic criteria in HLH-2004, has recently been reported as a good to excellent low-cost diagnostic test for adult HLH, with an area under the curve of 0.90 (95% confidence interval, 0.83-0.97) compared with an area under the curve of 0.78 (95% confidence interval, 0.67-0.88) for ferritin. Integration of a number of clinical features is required to confirm the diagnosis HLH in adults. Although a ferritin level in this range should also raise a strong suspicion of HLH in adults, hyperferritinemia is less specific. 26 Ferritin levels >10 000 µg/L are >90% sensitive and specific for HLH in children, although other criteria need to be met to make the diagnosis. 25 Ferritin values characteristic of HLH in adults are often >7000 to 10 000 µg/L and, rarely, may be >100 000 μg/L. Hyperferritinemia should always prompt inclusion of HLH in the differential diagnosis. Here, we present expert opinions derived from an interdisciplinary working group on adult HLH, sponsored by the Histiocyte Society, to facilitate knowledge transfer between physicians caring for pediatric and adult patients with HLH, with the aim to improve the outcome for adult patients affected by HLH. Therefore, dose reductions, individualized tailoring of treatment duration, and an age-dependent modified diagnostic approach are to be considered. ![]() Treatment algorithms targeting hyperinflammation are frequently based on pediatric protocols, such as HLH-94 and HLH-2004, which may result in overtreatment and unnecessary toxicity in adults. Another challenge in HLH diagnosis is that patients may present with a phenotype indistinguishable from sepsis or multiple organ dysfunction syndrome. For example, the HLH-2004 diagnostic criteria developed for children are commonly applied but are not validated for adults. Although helpful in some adult cases, this raises several challenges. Most information on the diagnosis and treatment of HLH comes from the pediatric literature. Secondary HLH is commonly triggered by infections or malignancies but may also be induced by autoinflammatory/autoimmune disorders, in which case it is called macrophage activation syndrome (MAS or MAS-HLH). The primary (genetic) form, caused by mutations affecting lymphocyte cytotoxicity and immune regulation, is most common in children, whereas the secondary (acquired) form is most frequent in adults. Hemophagocytic lymphohistiocytosis (HLH) is a severe hyperinflammatory syndrome induced by aberrantly activated macrophages and cytotoxic T cells.
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