|
|
Agency for Toxic Substances and Disease Registry
Case Studies in Environmental Medicine (CSEM)
Benzene Toxicity
Clinical Evaluation
In addition to a thorough medical history and physical examination, important factors in evaluating a patient potentially exposed to benzene are a detailed family history of blood dyscrasias including hematologic neoplasms, genetic hemoglobin abnormalities, bleeding abnormalities, and abnormal function of formed blood elements; an environmental history focusing on activities and possible sources of benzene exposure at home; and an occupational history, including past exposures to hematologic toxicants such as solvents, insecticides, and
arsenic. A history of ionizing radiation exposure, medications, and smoking should also be explored.
-
Acute benzene toxicity is characterized by CNS depression.
-
Symptoms may progress from light-headedness, headache, and euphoria to respiratory depression, apnea, coma, and death.
-
Benzene concentrations of about 20,000 ppm are fatal to humans within 5 to 10 minutes.
-
Ventricular fibrillation can occur due to myocardial sensitization.
"Benzol jag" is a term workers use to describe symptoms of confusion, euphoria, and unsteady gait associated with acute benzene exposure. Depending on the magnitude of the dose, persons who have ingested benzene may experience these effects 30 to 60 minutes after benzene ingestion. In one case report, an oral dose of 10 milliliters was reported to produce staggering gait, vomiting, tachycardia, pneumonitis, somnolence, delirium, seizures, coma, and death. Other symptoms include bronchial and laryngeal irritation after inhalation. Pulmonary edema has been reported. Ingestion may cause substernal pain; cough; hoarseness; and burning of the mouth, pharynx, and esophagus shortly after ingestion. It may also cause stomach pain, nausea, and vomiting.
-
Symptoms of chronic benzene exposure may be nonspecific, such as fever, bleeding, fatigue, and anorexia.
Early symptoms of chronic benzene exposure are often nonspecific but show marked individual variability. By the time a physician is consulted, the bone marrow may have been significantly affected. For example, conditions that first bring the patient to medical attention are typically fever due to infection or manifestations of thrombocytopenia, such as hemorrhagic diathesis with bleeding from the gums, nose, skin, gastrointestinal tract, or elsewhere; fatigue; and anorexia.
The clinical picture of patients chronically exposed to benzene was well described in 1938 in a cohort study of about 300 workers in the rotogravure printing industry. At that time, ink solvents and thinners containing 75 to 80% benzene by volume were used in the pressroom. Initial physical examination of the workers was relatively unrevealing, but of those tested, 22 persons had severe hematologic abnormalities. Followup of the workers a year after cessation of exposure suggested that the effects of benzene can persist or can evolve over time. However, most patients recover after exposure ceases.
-
Hematologic abnormalities are the primary concern in benzene exposure.
The laboratory evaluation of benzene-exposed persons should include the following: complete blood count with differential, Hct, Hgb, erythrocyte count, erythrocyte indices (i.e., MCV, MCH, and MCHC), and platelet count. Plasma folate and vitamin B12 levels may be used to rule out megaloblastic anemia if the MCV is elevated. These laboratory tests will detect hematologic abnormalities that have been associated with relatively high levels of exposure to benzene. Persons with blood dyscrasias that persist after removal from exposure should be evaluated by a hematologist. Bone marrow aspiration and biopsy may be useful in narrowing the differential diagnosis in some cases.
-
Benzene measurements in blood and breath are generally not clinically useful in nonoccupational settings.
Measurement of benzene in breath and blood can be useful in certain occupational settings. Because of benzene's relatively short biologic half-life, blood benzene levels reflect exposure during the preceding hours, not cumulative body burden. A less invasive measurement of workplace exposure is benzene concentration in end-expired air. A study has shown that workers exposed to benzene at levels between 0.2 and 4.1 ppm had measurable benzene vapor in their breath 16 hours after exposure and showed a progressive buildup of benzene in their expired air during the workweek.
-
Because of the contributions of background exposure, urinary phenol concentrations may not accurately reflect low occupational benzene exposures (e.g., <10 ppm).
Urinary phenol concentrations generally correlate well with benzene exposure to concentrations above 10 ppm. Workplace exposure to 10 ppm for 8 hours typically produces a postshift urinary phenol level of 45 to 50 mg/liter (mg/L), but excretion of phenol from dietary and other background sources (e.g., Pepto-Bismol) can obscure the contribution to urinary phenol of exposure air levels below 10 ppm. Under circumstances of such low-level exposure, urinary phenol levels are unreliable. Unexposed persons rarely have urinary phenol levels greater than 20 mg/L. Other benzene metabolites, such as muconic acid and phenyl mercapturic acid, are also used as indicators of exposure to benzene. Analysis of urinary muconic acid appears to be a better indicator than phenol for chronic, low-level benzene exposure. However, it is not specific for benzene exposure. Phenylmercapturic acid concentrations in the urine are highly specific parameters, although data concerning a dose-response relationship between phenylmercapturic acid production and benzene uptake in workers are not yet available.
-
MCV and lymphocyte count may aid in the diagnosis of benzene toxicity.
An increase in MCV, a decrease in total lymphocytes, and decreases in red blood cells and white blood cells may be early signs of benzene toxicity. A finding of benzene-induced hematotoxicity in a patient should trigger consideration that this represents a sentinel event, indicating that other persons may have been similarly exposed.
-
A bone marrow aspiration and biopsy will aid in identifying aplastic anemia.
If aplastic anemia is suspected, a bone marrow aspiration and biopsy should be performed. Aspiration of the marrow space often produces no sample (i.e., dry tap) in patients with aplastic anemia. However, a dry tap is not diagnostic of aplastic anemia; therefore, a biopsy specimen also should be obtained and examined for architecture and cellularity. In aplastic anemia, only the empty reticular meshwork of the marrow is evident; fat cells replace all or most of the hematopoietic tissues.
Islands of residual hematopoiesis may be seen, but the overall cellularity typically is less than 25%. Chromosomal changes consistent with myelodysplasia are seen on cytogenetic analysis.
- What should be included in the problem list of the patient described in the case study?
- What additional laboratory testing would you recommend?
Previous Section
Next Section
|
