Neutropenic fever

Neutropenia is a reduced absolute neutrophil count that raises infection risk sharply once the count falls below 500/microL, most often from chemotherapy or another marrow-suppressing or idiosyncratic drug. Diagnosis rests on a repeat CBC with differential and smear review followed by a directed search for cause, and management centers on stopping the offending agent, treating any underlying disease, and using G-CSF and neutropenic precautions when the count is low or the patient is febrile.

Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection, identified by an acute rise in SOFA score of 2 points or more in a patient with known or suspected infection. Survival depends on recognizing the pattern early and completing the hour-1 bundle: lactate, blood cultures before antibiotics, broad-spectrum antibiotics such as cefepime 2 g IV every 8 hours, and 30 mL/kg crystalloid for hypotension or a lactate of 4 mmol/L or higher.

Acute myeloid leukemia is a clonal proliferation of myeloid precursors that fails to differentiate, defined by myeloblasts at or above 20% of the bone marrow or blood, and it presents with cytopenias from marrow replacement plus, in acute promyelocytic leukemia, a coagulopathic emergency. Diagnosis rests on marrow blast count, immunophenotype, and cytogenetic and molecular testing that set both classification and risk, while treatment is intensive induction chemotherapy or ATRA-arsenic trioxide for APL, followed by risk-adapted consolidation.

Acute lymphoblastic leukemia is a clonal proliferation of lymphoid precursor blasts that replace the bone marrow, the most common cancer in children, diagnosed when TdT-positive lymphoblasts make up 20% or more of the marrow and classified by flow cytometry immunophenotype and cytogenetics. Treatment is multi-phase chemotherapy (induction, consolidation, CNS prophylaxis, maintenance for up to 2 years), with a tyrosine kinase inhibitor added for Philadelphia-chromosome-positive disease and aggressive tumor lysis prophylaxis at the start of therapy.

Non-Hodgkin lymphoma is a heterogeneous group of B-cell (about 85%) and T-cell lymphoid malignancies that spread noncontiguously and often involve extranodal sites, ranging from indolent follicular lymphoma to aggressive diffuse large B-cell lymphoma to highly aggressive Burkitt lymphoma. Diagnosis requires excisional or core biopsy with flow cytometry and cytogenetics, Ann Arbor staging with PET-CT, and treatment is subtype-specific, from observation to R-CHOP to intensive Burkitt regimens with aggressive tumor lysis and CNS prophylaxis.

Invasive aspergillosis is an angioinvasive mold infection of neutropenic and immunosuppressed hosts that begins in the respiratory tract and disseminates hematogenously, diagnosed with CT, galactomannan, and biopsy, and treated first-line with voriconazole.

Candida species cause a spectrum from mucocutaneous disease (thrush, esophagitis, vulvovaginal candidiasis, intertrigo) to candidemia and invasive candidiasis, the fourth most common cause of bloodstream infection with 30-40% mortality. Diagnosis of invasive disease requires recognizing risk factors because only 40-60% of infected patients have positive blood cultures, and initial therapy is an echinocandin with prompt catheter removal.

Tumor lysis syndrome is a metabolic oncologic emergency in which massive tumor cell breakdown, spontaneous or chemotherapy-induced, releases potassium, phosphate, and nucleic acids into the blood, producing hyperuricemia, hyperkalemia, hyperphosphatemia, and secondary hypocalcemia that can precipitate acute kidney injury, arrhythmia, seizure, and death. Risk-stratified prophylaxis with hydration plus allopurinol or rasburicase before chemotherapy, and aggressive correction of electrolytes with renal replacement therapy when needed, are the cornerstones of management.