Case Presentation: 46 year-old-male with no past medical history presented with 1-day-history of dyspnea on exertion, productive cough, and fever. The patient also complained of several weeks of generalized weakness and lower back pain radiating down his legs. Upon initial evaluation, a chest x-ray was normal and a rapid viral panel was positive for human metapneumovirus prompting admission for supportive care. Laboratory data was remarkable for anemia with a hemoglobin of 8.1 gm/dL, thrombocytopenia with platelets of 40 K/uL in addition to an elevated total bilirubin of 2.6 with a normal direct bilirubin. Further work-up of his anemia revealed evidence of hemolysis with a low reticulocyte count and an increased number of blasts on peripheral smear. This prompted a bone marrow biopsy, which was consistent with acute B-cell lymphoblastic leukemia.
Discussion: Acute lymphoblastic leukemia (ALL) is characterized by overproduction and accumulation of lymphoblasts in the bone marrow. It is more often a disease seen in childhood but can also be found in adults. The overall incidence of ALL follows a bimodal distribution in the United States: 1.5 per 100,000 with peaks between 2-5 years of age, and again after age 50. Patients may present with fevers, night sweats and weight loss, easy bleeding, bruising, dyspnea and infections but in some cases, extremity and joint pain may be the only symptoms. Lab abnormalities in ALL include normocytic anemia associated with hemolysis, reticulocytopenia, neutropenia and thrombocytopenia. A peripheral smear and bone marrow biopsy will be be significant for increased blast cells. Because these blasts lack specific morphologic and cytochemical features, the diagnosis of ALL depends on immunophenotyping by flow cytometry and cytogenetic analysis. Immunophenotype serves to characterize ALL into early Pre-B-cell, Pre-B-cell, mature B-cell, and T-cell ALL based on expression of certain antigens on leukemic cells. Cytogenetics is one of the most important prognostic factors for ALL and allows evaluation of specific genetic abnormalities. For example, the Philadelphia Chromosome t(9;22) is the most frequent genetic rearrangement in adult ALL. It is present in 25% of adults, but only 3% of children, and is a poor prognosticator. Overall, ALL is a highly curable disease in children with cure rates ranging from 60% to 85%. However, only about 20% of adults are cured with about 75% achieving complete remission.
Conclusions: The clinical features of viral infections may mimic those of ALL. This case was unique in that the patient was admitted for symptoms of an upper respiratory tract infection confirmed by the presence of human metapneumovirus, but a thorough workup of his underlying anemia led to the diagnosis of ALL. This case highlights the importance of recognizing various presentations of ALL especially when least expected.