Prolymphocytic leukemia, encompassing both T-cell and B-cell subtypes, is one of the most aggressive forms of leukemia characterized by a rapidly deteriorating clinical course and poor survival rates. Hepatosplenomegaly, marked leukocytosis, and cutaneous lesions such as nodules and a maculopapular rash are some of the main symptoms. Laboratory assessment, examination of a peripheral blood smear, and a histopathological examination with immunohistochemistry are key components of the diagnostic workup.
Described as a type of leukemia having a rather poor prognosis, prolymphocytic leukemia (PLL) is a rare lymphoid malignancy of mature T or B cells    . Prolymphocytic leukemia is primarily encountered in elderly patients, with a slight predisposition toward male gender   . In addition to the aggressive nature of this malignant disease, a very limited response to chemotherapy, and frequent relapses, a delayed diagnosis is an equally important reason for such low survival rates - 5-year survival established around 20%, while median survival is 4-7.5 months and 3 years for T-cell PLL and B-cell PLL, respectively    . Although several reports have documented a rather slow clinical course of prolymphocytic leukemia, or even asymptomatic patients  , symptoms develop rapidly in the majority of cases, with splenomegaly (sometimes accompanied by hepatomegaly) and lymphadenopathy being the most prominent   . In a small, but a significant number of cases, skin lesions in the form of nodules, a maculopapular rash (either generalized or local), or erythrodermia in rare cases, are observed, and primarily appear in T-cell PLL   . Periorbital or conjunctival edema is another important feature of prolymphocytic leukemia and is more commonly seen in T-cell PLL . Pleuroperitoneal serous effusions are rare complications seen in T-cell PLL, but are absent in B-cell PLL, which might be used as a distinguishing clinical feature   .
A thorough diagnostic workup is mandatory in order to identify prolymphocytic leukemia in its early stages. Firstly, a detailed patient history must be obtained, during which the course, as well as the progression of symptoms, must be noted. Furthermore, palpation of the abdomen, as a component of the physical examination, will confirm the presence of splenomegaly and indicate additional testing. A complete blood count (CBC) is the cornerstone of the laboratory workup, showing profound lymphocytosis (over 100 × 109/L), whereas anemia/thrombocytopenia is observed in approximately 50% of cases   . Circulating levels of lactate dehydrogenase (LDH) are also elevated . Once there is valid clinical suspicion of a lymphoproliferative process, examination of the peripheral blood smear needs to be carried out, where the presence of medium-sized prolymphocytes with intense nongranular basophilic cytoplasm containing protrusions or blebs and large (often irregular-shaped) nuclei with single prominent nucleoli is highly suggestive of a T-cell prolymphocytic leukemia   . A somewhat larger size of prolymphocytes, however, is characteristic for B-cell PLL . Recognizing B-cell PLL may be challenging, because of its rather rare occurrence and similar findings compared to other mature B-cell disorders (eg. mantle cell lymphoma) . To solidify the diagnosis, immunohistochemistry and phenotyping using flow cytometry is recommended - CD2, CD3, CD5 and CD7 positivity is expressed by T-cell PLL, whereas CD19, CD20, and CD22 positivity, as well as strong expression of surface membrane immunoglobulin, or SMIg, is typical for B-cell PLL . For T-cell PLL, expression of T-cell receptor-1 (TCL-1) protein was examined and proposed as a prognostic factor in determining overall survival  . Lymph node or spleen biopsies are indicated only if inconclusive findings are obtained on peripheral blood smears or when the exact type of lymphoid malignancy is not determined  . A bone marrow biopsy will show diffuse infiltration of prolymphocytes and active hematopoiesis .