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Emergency and Acute Medicine – Lymphocytosis
Overview and Definition
Lymphocytosis is defined as an absolute lymphocyte count greater than 4,000 cells/mm³ in peripheral blood. It may be reactive or neoplastic in origin. Reactive lymphocytosis is caused by infectious or noninfectious conditions, whereas neoplastic lymphocytosis reflects underlying hematologic malignancy. Infectious causes include viral, bacterial, protozoal, and parasitic diseases, while noninfectious causes include drugs, autoimmune disorders, and certain endocrinopathies. Atypical lymphocytes are non-neoplastic, activated lymphocytes that appear in response to immunologic stimulation; they are typically large, with nucleoli, irregular cytoplasm, and may appear to “indent” surrounding red blood cells on smear.
Clinical Approach
History and physical examination are essential to distinguish reactive from neoplastic lymphocytosis. Age is an important clue: acute EBV infection is common in children and young adults, while chronic lymphocytic leukemia is more common after the fifth decade. Assess symptom duration, vaccination history, prior illnesses, and medication use. Evaluate risk factors for HIV and tuberculosis, including sexual exposure, intravenous drug use, close contacts, travel, homelessness, and institutionalization. A detailed travel history should assess risk for food-, water-, and arthropod-borne infections. Physical examination should focus on lymphadenopathy and organ involvement such as hepatomegaly or splenomegaly. Many clinically stable patients without systemic toxicity can be evaluated as outpatients. Peripheral blood smears should be reviewed by experienced personnel, as atypical lymphocytes may be subtle.
Epidemiology
Lymphocytosis is common across many clinical conditions. Evidence of prior EBV infection is present in over 90% of adults. Primary EBV infection is frequent and often asymptomatic in children. CMV seroprevalence increases with age, exceeding 90% in adults over 80 years. Acute HIV infection may present with atypical lymphocytosis and a mononucleosis-like illness. Tuberculosis remains highly prevalent worldwide, with a large reservoir of latent infection.
Etiology
Common infectious causes include EBV, CMV, HIV, adenovirus, influenza, hepatitis A and B, measles, mumps, rubella, dengue, rickettsial infections, pertussis, tuberculosis, Bartonella, Brucella, syphilis, Q fever, Mycoplasma pneumoniae, toxoplasmosis, malaria, and babesiosis. Noninfectious causes include drug and toxic reactions, post-perfusion syndrome, immunizations, radiation exposure, endocrine disorders such as thyrotoxicosis or adrenal insufficiency, autoimmune diseases, smoking, and stress-related catecholamine release. Malignant causes include acute and chronic lymphocytic leukemia, lymphomas, hairy cell leukemia, and paraneoplastic syndromes. Other causes include sarcoidosis, thymoma, myasthenia gravis, Guillain–Barré syndrome, serum sickness, graft rejection, and inherited immune disorders.
Clinical Features
Acute EBV, CMV, or HIV infection may present with fever, lymphadenopathy, pharyngitis, fatigue, and anorexia. EBV typically causes exudative pharyngitis and hepatosplenomegaly, while CMV more often presents with prolonged fever and less prominent organomegaly. Cat-scratch disease presents with localized lymphadenopathy near the inoculation site. Cycling (Pel–Ebstein) fevers raise concern for Hodgkin lymphoma. Generalized lymphadenopathy is seen in many infections, leukemias, lymphomas, and sarcoidosis. Massive splenomegaly suggests myeloproliferative disorders, lymphomas, malaria, visceral leishmaniasis, or storage diseases. Viral hepatitis may present with jaundice and right upper quadrant tenderness.
Diagnostic Evaluation
Peripheral blood smear review is essential, and prior blood counts should be reviewed to assess chronicity. EBV infection is characterized by atypical lymphocytosis, positive heterophile antibody testing, and mild transaminitis. The Monospot test is highly specific and moderately sensitive. EBV serology distinguishes acute from past infection. CMV diagnosis relies on IgM and IgG serology, with PCR reserved for immunocompromised patients. HIV testing includes antigen–antibody screening with confirmatory testing; PCR is required in suspected acute infection. Toxoplasmosis is diagnosed by serology. Respiratory viruses such as influenza are detected by nasopharyngeal swab, with PCR offering the highest sensitivity. If malignancy is suspected, further evaluation may include flow cytometry, bone marrow biopsy, and cytogenetic studies. Imaging is reserved for clinical indications such as suspected pneumonia, organomegaly, or focal neurologic findings.
Management
Treatment is directed at the underlying cause. Uncomplicated EBV infection requires supportive care only. Patients with hepatosplenomegaly should avoid contact sports for up to two months due to risk of splenic rupture. Antibiotics such as ampicillin may cause rash in EBV infection and should be avoided. CMV treatment is generally reserved for immunocompromised patients. HIV infection requires antiretroviral therapy under specialist care.
Medications
Supportive therapy with acetaminophen or NSAIDs is appropriate for uncomplicated viral infections. Corticosteroids may be used for airway compromise in EBV. Antiviral therapy for CMV includes ganciclovir or valganciclovir in selected patients. Herpesvirus infections may be treated with acyclovir or valacyclovir. Influenza is treated with neuraminidase inhibitors when indicated.
Follow-Up and Prognosis
Patients should be counseled regarding warning signs and complications, particularly in EBV infection. Liver enzymes should be monitored until normalization. Persistent or unexplained lymphocytosis warrants hematology consultation to exclude malignancy.
Overview and Definition
Lymphocytosis is defined as an absolute lymphocyte count greater than 4,000 cells/mm³ in peripheral blood. It may be reactive or neoplastic in origin. Reactive lymphocytosis is caused by infectious or noninfectious conditions, whereas neoplastic lymphocytosis reflects underlying hematologic malignancy. Infectious causes include viral, bacterial, protozoal, and parasitic diseases, while noninfectious causes include drugs, autoimmune disorders, and certain endocrinopathies. Atypical lymphocytes are non-neoplastic, activated lymphocytes that appear in response to immunologic stimulation; they are typically large, with nucleoli, irregular cytoplasm, and may appear to “indent” surrounding red blood cells on smear.
Clinical Approach
History and physical examination are essential to distinguish reactive from neoplastic lymphocytosis. Age is an important clue: acute EBV infection is common in children and young adults, while chronic lymphocytic leukemia is more common after the fifth decade. Assess symptom duration, vaccination history, prior illnesses, and medication use. Evaluate risk factors for HIV and tuberculosis, including sexual exposure, intravenous drug use, close contacts, travel, homelessness, and institutionalization. A detailed travel history should assess risk for food-, water-, and arthropod-borne infections. Physical examination should focus on lymphadenopathy and organ involvement such as hepatomegaly or splenomegaly. Many clinically stable patients without systemic toxicity can be evaluated as outpatients. Peripheral blood smears should be reviewed by experienced personnel, as atypical lymphocytes may be subtle.
Epidemiology
Lymphocytosis is common across many clinical conditions. Evidence of prior EBV infection is present in over 90% of adults. Primary EBV infection is frequent and often asymptomatic in children. CMV seroprevalence increases with age, exceeding 90% in adults over 80 years. Acute HIV infection may present with atypical lymphocytosis and a mononucleosis-like illness. Tuberculosis remains highly prevalent worldwide, with a large reservoir of latent infection.
Etiology
Common infectious causes include EBV, CMV, HIV, adenovirus, influenza, hepatitis A and B, measles, mumps, rubella, dengue, rickettsial infections, pertussis, tuberculosis, Bartonella, Brucella, syphilis, Q fever, Mycoplasma pneumoniae, toxoplasmosis, malaria, and babesiosis. Noninfectious causes include drug and toxic reactions, post-perfusion syndrome, immunizations, radiation exposure, endocrine disorders such as thyrotoxicosis or adrenal insufficiency, autoimmune diseases, smoking, and stress-related catecholamine release. Malignant causes include acute and chronic lymphocytic leukemia, lymphomas, hairy cell leukemia, and paraneoplastic syndromes. Other causes include sarcoidosis, thymoma, myasthenia gravis, Guillain–Barré syndrome, serum sickness, graft rejection, and inherited immune disorders.
Clinical Features
Acute EBV, CMV, or HIV infection may present with fever, lymphadenopathy, pharyngitis, fatigue, and anorexia. EBV typically causes exudative pharyngitis and hepatosplenomegaly, while CMV more often presents with prolonged fever and less prominent organomegaly. Cat-scratch disease presents with localized lymphadenopathy near the inoculation site. Cycling (Pel–Ebstein) fevers raise concern for Hodgkin lymphoma. Generalized lymphadenopathy is seen in many infections, leukemias, lymphomas, and sarcoidosis. Massive splenomegaly suggests myeloproliferative disorders, lymphomas, malaria, visceral leishmaniasis, or storage diseases. Viral hepatitis may present with jaundice and right upper quadrant tenderness.
Diagnostic Evaluation
Peripheral blood smear review is essential, and prior blood counts should be reviewed to assess chronicity. EBV infection is characterized by atypical lymphocytosis, positive heterophile antibody testing, and mild transaminitis. The Monospot test is highly specific and moderately sensitive. EBV serology distinguishes acute from past infection. CMV diagnosis relies on IgM and IgG serology, with PCR reserved for immunocompromised patients. HIV testing includes antigen–antibody screening with confirmatory testing; PCR is required in suspected acute infection. Toxoplasmosis is diagnosed by serology. Respiratory viruses such as influenza are detected by nasopharyngeal swab, with PCR offering the highest sensitivity. If malignancy is suspected, further evaluation may include flow cytometry, bone marrow biopsy, and cytogenetic studies. Imaging is reserved for clinical indications such as suspected pneumonia, organomegaly, or focal neurologic findings.
Management
Treatment is directed at the underlying cause. Uncomplicated EBV infection requires supportive care only. Patients with hepatosplenomegaly should avoid contact sports for up to two months due to risk of splenic rupture. Antibiotics such as ampicillin may cause rash in EBV infection and should be avoided. CMV treatment is generally reserved for immunocompromised patients. HIV infection requires antiretroviral therapy under specialist care.
Medications
Supportive therapy with acetaminophen or NSAIDs is appropriate for uncomplicated viral infections. Corticosteroids may be used for airway compromise in EBV. Antiviral therapy for CMV includes ganciclovir or valganciclovir in selected patients. Herpesvirus infections may be treated with acyclovir or valacyclovir. Influenza is treated with neuraminidase inhibitors when indicated.
Follow-Up and Prognosis
Patients should be counseled regarding warning signs and complications, particularly in EBV infection. Liver enzymes should be monitored until normalization. Persistent or unexplained lymphocytosis warrants hematology consultation to exclude malignancy.
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