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"hemophagocytic lymphohistiocytosis"[MeSH Terms] AND treatment
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Hemophagocytic Lymphohistiocytosis (HLH)
Definition and Core Pathophysiology
HLH is a life-threatening hyperinflammatory syndrome caused by uncontrolled activation of CD8+ T lymphocytes, NK cells, and macrophages/histiocytes, leading to a cytokine storm and multi-organ damage (Robbins & Kumar Basic Pathology, p. 401; Harrison's Principles of Internal Medicine 22E).
The central mechanism: inherited or acquired defects impair the cytolytic (killing) function of cytotoxic T cells and NK cells. Because these "killer lymphocytes" cannot efficiently destroy their targets (e.g., virus-infected cells), they remain engaged with target cells for abnormally long periods, driving excessive release of IFN-γ. This overdrives macrophage activation, producing toxic levels of proinflammatory cytokines (TNF, IL-6, IL-18, soluble IL-2 receptor/CD25) - a picture that clinically mimics sepsis or systemic inflammatory response syndrome (Robbins Basic Pathology, p. 401). Activated macrophages then phagocytose red cells, platelets, and nucleated marrow precursors ("hemophagocytosis"), which is why the syndrome is also called macrophage activation syndrome (MAS) when triggered by autoimmune disease.
Classification
HLH is divided into primary (genetic) and secondary (acquired) forms, though the clinical phenotype converges (Harrison's, Ch. 68, Jan-Inge Henter):
Primary HLH - Mendelian conditions
- Familial HLH (FHL) subtypes from lymphocyte cytotoxic defects:
- FHL2 - PRF1 (perforin deficiency, ~30% of familial cases)
- FHL3 - UNC13D (Munc13-4 deficiency, ~30%)
- FHL4 - STX11 (syntaxin-11 deficiency, ~10%)
- FHL5 - STXBP2 (Munc18-2 deficiency, ~20%)
- Rare: FAAP24, RHOG mutations
- HLH with partial albinism (pigmentary disorders with cytotoxic defects): Chédiak-Higashi syndrome (giant lysosomal granules, progressive neurologic disease), Griscelli syndrome type 2, Hermansky-Pudlak syndrome type II
- X-linked lymphoproliferative disease (XLP1, SH2D1A/SAP deficiency) and XLP2 (BIRC4/XIAP deficiency) - both classically triggered by EBV infection
- Inflammasome/other Mendelian disorders: NLRC4 gain-of-function, lysinuric protein intolerance, Wolman disease
Secondary (non-Mendelian) HLH
- Infection-associated: viral (EBV is the classic and most common trigger), bacterial, parasitic, fungal
- Malignancy-associated (especially peripheral T-cell/NK-cell lymphomas, or occurring during chemotherapy)
- Autoimmune-associated (MAS-HLH): systemic juvenile idiopathic arthritis, adult-onset Still's disease, SLE, vasculitis
- Transplant-associated HLH
Primary HLH predominantly affects infants and children (often presenting in the first year of life, occasionally at birth); secondary HLH is far more common in adults.
Clinical Features
- Fever, hepatosplenomegaly, lymphadenopathy, edema
- Cytopenias (affecting ≥2 of: hemoglobin, platelets, neutrophils)
- Neurologic manifestations (irritability, seizures, altered consciousness - CNS involvement is common and prognostically important)
- Coagulopathy, sometimes progressing to DIC
- Elevated liver enzymes, hepatic dysfunction
- In severe cases: multi-organ failure and death if untreated
Key Laboratory/Diagnostic Findings
- Markedly elevated ferritin (classically >10,000 μg/L is highly suggestive, though lower levels don't exclude it)
- Hypertriglyceridemia
- Hypofibrinogenemia
- Elevated soluble IL-2 receptor (sCD25) - a marker of T-cell activation
- Low or absent NK cell cytotoxicity; reduced circulating NK cells and CD8+ T cells
- Hemophagocytosis on bone marrow or CSF examination (macrophages engulfing RBCs, platelets, and nucleated marrow cells) - supportive but neither required nor sufficient alone for diagnosis
- Functional assays (e.g., CD107a degranulation assay) and genetic testing help identify genetically determined HLH, along with assessment of intracellular perforin expression
Diagnosis is clinical, built on this constellation of features (fever, hepatosplenomegaly, cytopenias, hypofibrinogenemia/hypertriglyceridemia, hyperferritinemia, elevated T-cell activation markers, hemophagocytic features) rather than any single test.
Treatment
- Immunosuppression/chemotherapy: Etoposide-based regimens (e.g., HLH-94/HLH-2004 protocols combining etoposide, dexamethasone, +/- cyclosporine) remain a backbone of therapy, particularly in genetic HLH and severe presentations (Harrison's, Ch. 68/362).
- Targeted biologics: anti-T-cell antibodies; agents targeting the IFN-γ pathway (e.g., emapalumab, an anti-IFN-γ monoclonal antibody) and JAK1/2 inhibition, which interrupt the cytokine-driven amplification loop.
- Hematopoietic stem cell transplantation (HSCT): offers the only chance of cure for patients with inherited (genetic) HLH, since the underlying cytotoxic lymphocyte defect persists otherwise.
- Treat the trigger: for secondary HLH, addressing the underlying infection, malignancy, or autoimmune disease is essential alongside immunosuppression.
- Treatment is tailored to etiology, but outcomes are often poor even with treatment, especially in delayed diagnosis or CNS involvement.
Recent Evidence (surfacing per protocol - may refine/update the above)
A few recent systematic reviews/meta-analyses are worth flagging since they touch directly on treatment choices discussed above:
- A 2025 systematic review/meta-analysis (PMID: 39955467) specifically assessed etoposide effectiveness in adult HLH - useful since much of the etoposide evidence base (HLH-94/2004) was pediatric-derived; adult outcomes and optimal dosing may differ.
- A 2024 systematic review (PMID: 38934172) evaluated rituximab as a therapeutic strategy in HLH, particularly EBV-driven HLH, an option not covered in the textbook excerpts above (targets EBV-infected B cells rather than the cytokine storm directly).
- A 2023 meta-analysis (PMID: 36579732) looked at treatment and mortality in critically ill children with HLH, relevant for ICU-level decision-making.
These don't contradict the textbook framework but add more granular, population-specific outcome data (adults, EBV-driven disease, pediatric ICU) that a clinician managing a real case should review directly if treatment decisions are being made.
51 yr old Patient with recurrent hypoglycaemic attacks
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"hypoglycemia"[MeSH Terms] AND diagnosis
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Endocrine Society adult hypoglycemic disorders evaluation Whipple triad 72 hour fast insulin C peptide
A diagnosis cannot be made from age and recurrent attacks alone. The key distinction is whether episodes occur during fasting, after meals, or in a person using glucose-lowering drugs.
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Which details are available for this patient?
Hemophagocytic Lymphohistiocytosis (HLH)
Definition and Core Pathophysiology
HLH is a life-threatening hyperinflammatory syndrome caused by uncontrolled activation of CD8+ T lymphocytes, NK cells, and macrophages/histiocytes, leading to a cytokine storm and multi-organ damage (Robbins & Kumar Basic Pathology, p. 401; Harrison's Principles of Internal Medicine 22E).
The central mechanism: inherited or acquired defects impair the cytolytic (killing) function of cytotoxic T cells and NK cells. Because these "killer lymphocytes" cannot efficiently destroy their targets (e.g., virus-infected cells), they remain engaged with target cells for abnormally long periods, driving excessive release of IFN-γ. This overdrives macrophage activation, producing toxic levels of proinflammatory cytokines (TNF, IL-6, IL-18, soluble IL-2 receptor/CD25) - a picture that clinically mimics sepsis or systemic inflammatory response syndrome (Robbins Basic Pathology, p. 401). Activated macrophages then phagocytose red cells, platelets, and nucleated marrow precursors ("hemophagocytosis"), which is why the syndrome is also called macrophage activation syndrome (MAS) when triggered by autoimmune disease.
Classification
HLH is divided into primary (genetic) and secondary (acquired) forms, though the clinical phenotype converges (Harrison's, Ch. 68, Jan-Inge Henter):
Primary HLH - Mendelian conditions
- Familial HLH (FHL) subtypes from lymphocyte cytotoxic defects:
- FHL2 - PRF1 (perforin deficiency, ~30% of familial cases)
- FHL3 - UNC13D (Munc13-4 deficiency, ~30%)
- FHL4 - STX11 (syntaxin-11 deficiency, ~10%)
- FHL5 - STXBP2 (Munc18-2 deficiency, ~20%)
- Rare: FAAP24, RHOG mutations
- HLH with partial albinism (pigmentary disorders with cytotoxic defects): Chédiak-Higashi syndrome (giant lysosomal granules, progressive neurologic disease), Griscelli syndrome type 2, Hermansky-Pudlak syndrome type II
- X-linked lymphoproliferative disease (XLP1, SH2D1A/SAP deficiency) and XLP2 (BIRC4/XIAP deficiency) - both classically triggered by EBV infection
- Inflammasome/other Mendelian disorders: NLRC4 gain-of-function, lysinuric protein intolerance, Wolman disease
Secondary (non-Mendelian) HLH
- Infection-associated: viral (EBV is the classic and most common trigger), bacterial, parasitic, fungal
- Malignancy-associated (especially peripheral T-cell/NK-cell lymphomas, or occurring during chemotherapy)
- Autoimmune-associated (MAS-HLH): systemic juvenile idiopathic arthritis, adult-onset Still's disease, SLE, vasculitis
- Transplant-associated HLH
Primary HLH predominantly affects infants and children (often presenting in the first year of life, occasionally at birth); secondary HLH is far more common in adults.
Clinical Features
- Fever, hepatosplenomegaly, lymphadenopathy, edema
- Cytopenias (affecting ≥2 of: hemoglobin, platelets, neutrophils)
- Neurologic manifestations (irritability, seizures, altered consciousness - CNS involvement is common and prognostically important)
- Coagulopathy, sometimes progressing to DIC
- Elevated liver enzymes, hepatic dysfunction
- In severe cases: multi-organ failure and death if untreated
Key Laboratory/Diagnostic Findings
- Markedly elevated ferritin (classically >10,000 μg/L is highly suggestive, though lower levels don't exclude it)
- Hypertriglyceridemia
- Hypofibrinogenemia
- Elevated soluble IL-2 receptor (sCD25) - a marker of T-cell activation
- Low or absent NK cell cytotoxicity; reduced circulating NK cells and CD8+ T cells
- Hemophagocytosis on bone marrow or CSF examination (macrophages engulfing RBCs, platelets, and nucleated marrow cells) - supportive but neither required nor sufficient alone for diagnosis
- Functional assays (e.g., CD107a degranulation assay) and genetic testing help identify genetically determined HLH, along with assessment of intracellular perforin expression
Diagnosis is clinical, built on this constellation of features (fever, hepatosplenomegaly, cytopenias, hypofibrinogenemia/hypertriglyceridemia, hyperferritinemia, elevated T-cell activation markers, hemophagocytic features) rather than any single test.
Treatment
- Immunosuppression/chemotherapy: Etoposide-based regimens (e.g., HLH-94/HLH-2004 protocols combining etoposide, dexamethasone, +/- cyclosporine) remain a backbone of therapy, particularly in genetic HLH and severe presentations (Harrison's, Ch. 68/362).
- Targeted biologics: anti-T-cell antibodies; agents targeting the IFN-γ pathway (e.g., emapalumab, an anti-IFN-γ monoclonal antibody) and JAK1/2 inhibition, which interrupt the cytokine-driven amplification loop.
- Hematopoietic stem cell transplantation (HSCT): offers the only chance of cure for patients with inherited (genetic) HLH, since the underlying cytotoxic lymphocyte defect persists otherwise.
- Treat the trigger: for secondary HLH, addressing the underlying infection, malignancy, or autoimmune disease is essential alongside immunosuppression.
- Treatment is tailored to etiology, but outcomes are often poor even with treatment, especially in delayed diagnosis or CNS involvement.
Recent Evidence (surfacing per protocol - may refine/update the above)
A few recent systematic reviews/meta-analyses are worth flagging since they touch directly on treatment choices discussed above:
- A 2025 systematic review/meta-analysis (PMID: 39955467) specifically assessed etoposide effectiveness in adult HLH - useful since much of the etoposide evidence base (HLH-94/2004) was pediatric-derived; adult outcomes and optimal dosing may differ.
- A 2024 systematic review (PMID: 38934172) evaluated rituximab as a therapeutic strategy in HLH, particularly EBV-driven HLH, an option not covered in the textbook excerpts above (targets EBV-infected B cells rather than the cytokine storm directly).
- A 2023 meta-analysis (PMID: 36579732) looked at treatment and mortality in critically ill children with HLH, relevant for ICU-level decision-making.
These don't contradict the textbook framework but add more granular, population-specific outcome data (adults, EBV-driven disease, pediatric ICU) that a clinician managing a real case should review directly if treatment decisions are being made.A diagnosis cannot be made from age and recurrent attacks alone. The key distinction is whether episodes occur during fasting, after meals, or in a person using glucose-lowering drugs.In a 51-year-old with recurrent hypoglycaemic attacks, first confirm true hypoglycaemia, then determine whether it is due to drugs, critical illness, hormone deficiency, or endogenous excess insulin.
1. Confirm Whipple's triad
Investigate as a hypoglycaemic disorder when all three are present:
- Typical symptoms: sweating, tremor, palpitations, hunger, confusion, blurred vision, abnormal behavior, seizure, or loss of consciousness
- Documented low plasma glucose, usually <55 mg/dL (3.0 mmol/L) in a person without diabetes
- Symptoms resolve after glucose is raised
This is the recommended entry point in the Endocrine Society guideline.
2. Immediate safety
If confused, unconscious, fitting, unable to swallow, or glucose remains low despite oral intake, this needs emergency treatment now. Do not allow the patient to drive or remain alone.
If awake and able to swallow: take fast-acting carbohydrate such as glucose tablets, sugar-containing juice, or regular soft drink; recheck glucose after 15 minutes and repeat if still low. Follow with a longer-acting carbohydrate-containing snack/meal once recovered.
3. Important history
Ask specifically:
- Does the patient have diabetes?
- Any insulin, sulfonylurea, meglitinide, or other glucose-lowering medication? Also consider accidental, surreptitious, or wrong-dose exposure.
- Timing:
- Fasting/overnight or early-morning attacks suggest insulinoma or another fasting hypoglycaemia cause.
- After meals suggests postprandial/reactive hypoglycaemia, prior gastric surgery, or rarer hyperinsulinaemic states.
- Alcohol use, especially with poor intake
- Weight loss, abdominal symptoms, systemic illness, liver disease, kidney failure, sepsis
- Corticosteroid withdrawal, symptoms of adrenal insufficiency such as fatigue, hypotension, hyperpigmentation
- Personal/family history of pituitary disease, MEN1, pancreatic endocrine tumor
- Any recent bariatric/gastric surgery
4. Main differential diagnosis
A. Drug-induced hypoglycaemia
Most common in patients with diabetes:
- Insulin
- Sulfonylureas: glimepiride, gliclazide, glibenclamide, etc.
- Meglitinides
Also consider alcohol, quinolones, pentamidine, and drug interactions, particularly in renal or hepatic impairment.
B. Endogenous hyperinsulinism
This is important in a non-diabetic middle-aged adult with recurrent fasting attacks.
Insulinoma should be considered, especially if attacks occur after fasting, overnight, before breakfast, or improve rapidly with eating. It is a pancreatic neuroendocrine tumor producing inappropriate insulin.
Other causes:
- Sulfonylurea ingestion
- Factitious insulin administration
- Insulin autoimmune syndrome
- Non-insulinoma pancreatogenous hypoglycaemia syndrome, usually postprandial
C. Serious systemic illness
- Hepatic failure
- Renal failure
- Sepsis or severe infection
- Malnutrition/prolonged starvation
- Cardiac failure
D. Endocrine deficiency
- Adrenal insufficiency
- Hypopituitarism, especially ACTH/GH deficiency
E. Non-islet cell tumor hypoglycaemia
Large tumors can produce IGF-2, typically with weight loss or a known large tumor. Insulin and C-peptide are low during hypoglycaemia.
5. Essential investigation: obtain a "critical sample" during an attack
When plasma glucose is low and symptoms are present, collect blood before giving glucose if this does not delay emergency treatment:
- Laboratory plasma glucose
- Insulin
- C-peptide
- Proinsulin
- Beta-hydroxybutyrate (blood ketones)
- Sulfonylurea/meglitinide drug screen
- Insulin antibodies when appropriate
- Cortisol, with further adrenal testing if indicated
- Renal function, liver function, electrolytes, CBC
The biochemical pattern is more useful than imaging at first.
| During true hypoglycaemia | Likely interpretation |
|---|---|
| High insulin + high C-peptide + high proinsulin; low ketones | Endogenous hyperinsulinism, especially insulinoma, unless sulfonylurea screen is positive |
| High insulin + low C-peptide | Exogenous insulin exposure |
| High insulin + high C-peptide + positive sulfonylurea screen | Sulfonylurea/meglitinide effect |
| Low insulin + low C-peptide | Non-insulin causes: critical illness, adrenal insufficiency, malnutrition, liver disease, IGF-2 tumor, etc. |
A rise in glucose after IV glucagon during documented hypoglycaemia also supports insulin-mediated hypoglycaemia because hepatic glycogen has been preserved by insulin.
6. Provocative tests
If attacks are fasting-related
A supervised 72-hour fast in hospital is the reference investigation for suspected insulinoma/endogenous hyperinsulinism. The patient is monitored, and the critical sample is taken when symptomatic hypoglycaemia occurs.
Do not attempt a prolonged fast at home.
If attacks are after meals
A supervised mixed-meal test is preferred. An oral glucose tolerance test is generally not useful for diagnosing postprandial hypoglycaemia.
7. Localization only after biochemical confirmation
If endogenous hyperinsulinism is confirmed, localize an insulinoma using:
- Pancreatic contrast CT or MRI
- Endoscopic ultrasound
- Specialized functional imaging or selective arterial calcium stimulation testing when initial imaging is negative
Probable clinical thought in this case
If this 51-year-old is not diabetic, has recurrent fasting or early-morning episodes, and low glucose is documented, the leading diagnosis is insulinoma until proven otherwise. However, medication-related hypoglycaemia and occult sulfonylurea exposure must be excluded before labeling it insulinoma.
HLH is not a usual explanation for isolated recurrent hypoglycaemic episodes. HLH would generally produce prominent fever, cytopenias, liver dysfunction, organomegaly, and severe systemic illness.
Please provide the glucose value during an attack, diabetes/medication history, and whether episodes are fasting-related or post-meal.
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