PLL has no specific marker pattern, and its close relationship with CLL and MCL leads to an overlap in immunophenotype with those conditions. Diagnosis may be suggested by morphology, but requires correlation of clinical and immunophenotypic features and often additional knowledge of genetic or cytogenetic features.
- A rare disorder (<1% of B lymphoproliferative disorders) and must be distinguished from MCL and atypical CLL
- Typically lymphocytes are large with a single prominent nucleolus and relatively abundant blue cytoplasm
- These cells should form more than 55% of the neoplastic lymphocytes present on the film
- Generally the white cell count is high (>100x109/l) with an enlarged spleen
- Bone marrow is generally infiltrated, causing cytopenia and systemic symptoms
The cells vary in size considerably, and the larger cells are very distinctive with a single large nucleolus and basophilic cytoplasm. The chromatin is more condensed than would be typical for a blast cell. The majority of the lymphocytes shown share similar features (to a greater or lesser extent), although the smaller examples have less distinct nuceoli, and the smallest cells resemble a CLL lymphocyte. To make a diagnosis of PLL more than 55% of the abnormal lymphocytes should have the appearance of prolymphocytes. Also present on the film are numerous pale blue vesicles of varying size. These are not agranular platelets, these are cytoplasmic vesicles that have been released by the abnormal prolymphocytes. This "blebbing" process is more frequently described with T-PLL, but in this case the cells were B-lymphocytes.
IMMUNOPHENOTYPIC RECOGNITION OF PLL
Often morphologically and clinically distinctive, the close relationship between PLL and either CLL or MCL, results in immunophenotypic which can make the diagnosis difficult by immunophenotype alone. Cases should be viewed together with clinical and morphological features (and if required molecular or cytogenetic exclusion of other disorders).