Doctors classify the disease into different categories based on the number of enlarged lymph node regions and the underlying cause. There are four established subtypes of Castleman disease:

Unicentric Castleman disease
Unicentric Castleman disease (UCD) involves a single enlarged lymph node or multiple enlarged lymph nodes within a single region of the body that display microscopic features consistent with Castleman disease. It is also sometimes called localized Castleman disease.The exact cause of UCD is unknown, but appears to be due to a genetic change that occurs in the lymph node tissue, most similar to a benign tumor. In most cases of UCD, individuals exhibit no symptoms (asymptomatic). UCD symptoms tend to be mild and occur secondary to compression of surrounding structures by rapidly enlarging lymph nodes. Less commonly, some UCD patients can experience systemic inflammatory symptoms such as fever, fatigue, excessive sweating, weight loss, and skin rash as well as laboratory abnormalities such as low hemoglobin and elevated C-reactive protein. These symptoms are typically seen in MCD. Surgery is considered by experts to be the first-line treatment option for all cases of UCD. Sometimes, removing the enlarged lymph node(s) is not possible. If surgical excision is not possible, treatment is recommended for symptomatic patients. If symptoms are due to compression, then rituximab is recommended. If symptoms are due to an inflammatory syndrome, then anti-interleukin-6 (IL-6) therapy is recommended. If these treatments are not effective, then radiation may be needed.
Though all forms of MCD involve excessive production of cytokines and a cytokine storm, iMCD has important differences in symptoms, disease course, and treatment from POEMS-associated MCD and HHV-8-associated MCD. First line treatment for iMCD is anti-IL-6 therapy with siltuximab (or tocilizumab, if siltuximab is not available). Siltuximab is the only FDA-approved treatment for iMCD and patients who respond to siltuximab tend to have long-term responses. In critically ill patients, chemotherapy and corticosteroids are recommended if the patient is demonstrating disease progression while on siltuximab. Approximately half of iMCD patients do not improve with anti-IL-6 therapy. In patients where siltuximab is not effective, other treatments such as rituximab and sirolimus can be used.iMCD can be further sub-classified into three clinical subgroups:
iMCD with TAFRO Syndrome (iMCD-TAFRO): characterized by acute episodes of Thrombocytopenia, Anasarca, Fever, Renal dysfunction or mylefibrosis, and Organomegaly.iMCD with idiopathic plasmacytic lymphadenopathy (iMCD-IPL): characterized by thrombocytosis, hypergammaglobulinemia, and a more chronic disease course.iMCD, not otherwise specified (iMCD-NOS): is diagnosed in iMCD patients who do not have iMCD-TAFRO or iMCD-IPL. Pathology
Castleman disease is defined by a range of characteristic features seen on microscopic analysis (histology) of tissue from enlarged lymph nodes. Variations in the lymph node tissues of patients with CD have led to 4 histological classifications:

Plasmacytic: increased number of follicles with large hyperplastic germinal centers and sheetlike plasmacytosis (increased number plasma cells). Germinal centers may also show regressed features
Hyaline vascular: regressed germinal centers, follicular dendritic cell prominence or dysplasia, hypervascularity in interfollicular regions, sclerotic vessels, prominent mantle zones with an "onion-skin" appearance.