“Hairy kidney” in Erdheim-Chester Disease
A retroperitoneal tumour was discovered in a 62-year-old man undergoing abdominal ultrasound for the assessment of gallstones. The patient’s physical examination and the results of standard laboratory tests, including renal function tests, were both normal. Soft-tissue infiltration of the kidneys (Panel A, arrows), severe hydronephrosis of both kidneys, and mild splenomegaly were all seen on a computed tomographic (CT) urogram. A subsequent positron-emission tomography-CT scan revealed no evidence of hypermetabolic activity. Stents were implanted in both ureters, and a perinephric soft tissue core biopsy specimen was collected. The specimen’s histopathology indicated diffuse infiltration of pale-staining histiocytes (Panel B, arrows; hematoxylin and eosin staining) mixed with scattered lymphocytes and plasma cells. Immunohistochemistry revealed that the cells were significantly positive for CD68 while being negative for S100 and CD1a. Based on these findings, the patient was diagnosed with hairy kidney in Erdheim-Chester disease.
A BRAF V600E mutation was discovered by molecular testing. Erdheim-Chester disease is a non-Langerhans-cell histiocytosis characterised by sclerotic lesions in the long bones, which this patient did not have. This illness is also associated with a variety of extraosseous abnormalities, including retroperitoneal perinephric tissue infiltration, which results in a “hairy kidney” appearance on cross-sectional imaging, as seen in this patient. Vemurafenib, a specific inhibitor of the mutant BRAF V600E kinase, was initiated. The patient had no illness progression during a 1-year follow-up visit.
Erdheim-Chester illness is a non-Langerhans cell histiocytosis characterised by foamy histiocyte infiltration and fibrosis that can damage various organs, most notably the long bones. Renal involvement in this condition is typically shown as a histiocytic infiltrate into the perirenal fat. Histopathologic results from the right retroperitoneal region biopsies contained fibroadipose tissue fragments with a lymphohistiocytic infiltration.
The cytoplasm of these histiocytes was foamy, with irregular nuclei. Touton-like gigantic cells were also discovered. CD68 immunohistochemical staining confirmed the existence of histiocytes. Furthermore, the cells were negative for S100, excluding Langerhans cell histiocytosis. These findings allowed for a definitive diagnosis of ECD. There are no treatment guidelines for ECD. Interferon-a, targeted chemotherapy with serine/threonine protein kinase B-raf (BRAF) inhibitors, steroids, immunotherapy, radiotherapy, and surgery are among the treatments available. In this patient, BRAF testing was inconclusive, and chemotherapy was not initiated due to minor symptoms.
A rare, systemic and aggressive disease
ECD is an uncommon, systemic, and aggressive non-Langerhans histiocytosis with xanthomatous or xanthogranulomatous infiltration of foamy histiocytes and accompanying fibrosis, but no indication of cancer. There were roughly 500 recorded instances of ECD up till 2014. The aetiology and pathophysiology remain unknown, but a clonal neoplastic origin is assumed due to the presence of a V600E BRAF mutation in 54% of patients. Inflammation, with higher levels of IFN- and interleukins, also plays a role in pathogenesis. Non-Langerhans cell histiocytosis can also be caused by juvenile or adult-onset xanthogranuloma, xanthoma disseminatum, or Rosai-Dorfman disease.
ECD primarily affects men between the ages of 40 and 70, however paediatric cases have also been observed. Its diagnosis is difficult due to its variable presentation, which varies depending on the type and degree of organ involvement. ECD can be asymptomatic or manifest as a severe, multisystemic disease with potentially fatal signs.2 Table 1 lists the diagnostic criteria for ECD. In a case series of 53 ECD patients, 96% had skeletal damage although only 50% had bone pain. Skeletal involvement is the most common first presentation almost everywhere, although it was a late finding in our instance, coming after cardiac, renal, and neurological involvement had progressed to their ultimate phases.
ECD is frequently associated with retroperitoneal involvement, which affects 30% to 50% of individuals. Histiocytic infiltration and fibrosis can cause ureteral blockage and hydronephrosis, which can lead to kidney injury requiring ureteral stenting, as in this example.6 The presence of foamy cells, hairy kidney, and coated aorta, as well as the absence of plasma cells, vasculitis, and involvement of the pelvic ureter and inferior vena cava, help distinguish ECD from primary retroperitoneal fibrosis.