RDD is an idiopathic histiocytic proliferative disorder originally described by Rosai and Dorfman in 1969.2
The clinical features include massive painless lymphadenopathy, fever, and polyclonal hypergammaglobulinaemia. Most cases occur during the first or second decades of life, but any age group can be affected. With widespread geographic distribution and predisposition for black populations, extranodal involvement is reported in up to 25% of cases, with practically all organ systems affected, most commonly the eyes and ocular adnexa, head and neck region, upper respiratory tract, skin and subcutaneous tissue, and central nervous system.2,3
Other sites include the gastrointestinal tract, salivary glands, genitourinary tract, thyroid, and breast.3,4,5
Despite the apparent description of genitourinary disease, there has been to date only one report of testicular RDD, in a patient who developed the condition 12 years after the diagnosis of lymphoma.6
Another account in 1966 discussed a histiocytic proliferative disease manifesting as testicular enlargement, severe lymphadenopathy, transient hepatomegaly, hypergammaglobulinaemia, recurrent infections, and rheumatoid arthritis in a boy, and, although emperipolesis was not documented in the pathological specimens of the testis or lymph node, it is plausible that this case in fact represented RDD prior to its initial formal description,7
and thus the earliest example of testicular RDD.
The spleen and bone marrow are usually spared in RDD. For cases that are primarily nodal in presentation, about 43% also demonstrate at least one site of extranodal disease.3
The pathological features of RDD have been well described, and characteristic S100 positive histiocytes with emperipolesis remain the microscopic hallmark.2,3,4
In our patient, testicular RDD resulted in a clinical swelling for which a neoplasm was the prime consideration, supported by ultrasonographic examination. Even on microscopy, the presence of an admixture of histiocytes, lymphocytes, and plasma cells, together with occasional multinucleated giant cells, brought forth a differential diagnosis of xanthogranulomatous orchitis (XO), a lesion which has been reported more frequently than testicular RDD.8
XO is believed to be aetiologically related to immunological defects, chronic infection and abnormal phagocytosis. In fact, because of the difficulty of detecting emperipolesis in extranodal RDD3,4,9
as in our case, it is possible that a diagnosis of XO would have been rendered if a thorough search for emperipolesis or confirmation of S100 positive histiocytes had not been performed. The presence of rare multinucleated cells and several epithelioid histiocytes in our case is unusual for RDD, and may be explained as a response to disrupted seminiferous tubules, as an infective cause had been excluded. Malakoplakia was the other possible histological differential diagnosis, though the absence of Michaelis‐Guttman bodies essentially excluded this likelihood.
It was especially critical to exclude a testicular neoplasm, particularly since burnt out seminomas or seminomas with prominent accompanying inflammatory infiltrates may disclose few neoplastic cells obscured by inflammation.10
This can be readily addressed with immunostaining for PLAP and CD117. The lack of intratubular germ cell neoplasia was also a helpful feature.
The occurrence of RDD in our patient with diabetes and past pulmonary tuberculosis raises questions of whether these conditions are related. Our previous report of RDD of the breast included one patient with diabetes.5
Although the pathogenesis of RDD is still not fully elucidated, infective or immune mediated causes are plausible.11
The fact that diabetic patients are more susceptible to infections suggests possible immunological defects that may potentially predispose to RDD. The clinical course of RDD is generally benign, though there are reports of progressive disease.3,4
TAKE HOME MESSAGES
- Rosai‐Dorfman disease (RDD) is an idiopathic histiocytic proliferative disorder.
- Extranodal involvement is reported in up to 25% of cases, with practically all organ systems affected, but despite the apparent description of genitourinary disease, there has been to date only one report of testicular RDD.
- In our patient, the microscopic appearance suggested a diagnosis of xanthogranulomatous orchitis, showing the difficulty of diagnosing RDD.
In summary, testicular RDD is difficult to diagnose preoperatively, mimicking a testicular neoplasm clinicoradiologically. On microscopy, XO is a histological differential. A high index of suspicion is needed to identify typical histiocytes with emperipolesis. A possible relationship with systemic diseases such as diabetes needs to be explored.