In more than half of the cases, it is from gram-negative organisms. Atypical mycobacterial infections are common. Disseminated fungal infections and Pneumocystis carinii may occur in some cases. They are mononuclear cells with eccentric or centrally placed nuclei. CD22 stains at higher intensity in HCL than in normal B-cells.
Cytochemical evaluation is important for diagnostic confirmation of the morphologic findings.
The peripheral blood counts will show pancytopenia with decreased cell counts in all 3 cell lines. Anemia is usually severe and normochromic normocytic in character. The bone marrow aspirate is usually unsuccessful due to a dry tap. Infiltration by HCL of the bone marrow makes it difficult to aspirate cells through a needle. Core biopsy of the bone marrow shows a pattern of HCL infiltration with a single round or oval nucleus separated by abundant cytoplasm in a fine fibrillar network.