T-PLL is a rare aggressive disorder, accounting for 2% of the mature lymphoid leukemias. The median age at presentation is 65 years. It was originally classified in the 1970s as a variant of chronic lymphocytic leukemia, but later reclassified as a distinct entity.^2,3

The etiologic factors are unclear. The rare association with the human T-cell lymphotropic virus (HTLV) infection has been reported⁵; however, these cases likely represent adult T-cell leukemia/lymphoma (ATLL) in the current World Health Organization (WHO) classification.

Almost half of the patients present with hepatosplenomegaly and lymphadenopathy.⁶ Peripheral blood has a characteristic high lymphocytosis (>100 × 10⁹/L) with more than 90% of cells being prolymphocytes.^2,3,6,7,8 Cases with moderate lymphocytosis have also been described.⁴ A minority of patients (∼15%) may be asymptomatic at diagnosis, and this “indolent” phase can persist for a variable length of time, which may extend to several years. Skin involvement is identified in 20% to 50% of cases. It typically occurs in the setting of high white blood cell (WBC) counts and does not appear to impact on survival.^{9,10,11,12,13} The average 5-year survival without skin involvement is 13.2 months and ∼10 months with skin disease.¹¹ A slight male predominance is present in patients with skin disease.⁹ Concurrent involvement of the skin at the time of T-PLL diagnosis is frequent,¹⁴ and, in rare occasions, cutaneous involvement may herald the diagnosis of T-PLL.¹⁵

Facial erythema, periorbital edema, and conjunctival injection are common. Erythrodermic presentations have been reported.^{12,14,16,17,18,19} Cutaneous nodules tend to be linear, symmetrical in distribution, and have a petechial/purpuric quality²⁰ (Fig. 22-1).²¹ The clinical presentation may mimic dermatomyositis or lymphomatoid contact dermatitis^22,23 in some cases. Anemia and thrombocytopenia are seen in half of patients. Pleuroperitoneal effusions and central nervous system involvement may also occur.

T-PLL has a broad morphologic spectrum (Figs. 22-2 and 22-3). Most cases show a predominance of large prolymphocytes with round nuclei, condensed chromatin, prominent nucleoli, and basophilic, agranular cytoplasm. In some cases, cytoplasmic blebs can be present. In 20% of cases, neoplastic cells are small with inconspicuous nucleoli (“small cell variant”). In 5% of cases, lymphoma cells show cerebriform nuclei similar to those seen in Sézary syndrome (SS) (“cerebriform variant”).^1,2,3,6,8 In the bone marrow, there are diffuse and interstitial infiltrates, which are usually accompanied by reticulin fibrosis. In the lymph nodes, there is an abnormal paracortical expansion of neoplastic T cells.