Introduction
The hairy kidney is a pathognomic radiographic sign in Erdheim-Chester disease. Erdheim-Chester disease is rare, with only 500 reported cases until 2014. The diagnosis of Erdheim-Chester disease is based on histological and pathological features, but identification can be difficult due to its heterogeneous presentation. The presence of hairy kidney signs and coating aorta aids in diagnosis are discussed in the article.
What Is Erdheim-Chester Disease?
Erdheim-Chester disease is a rare form of non-Langerhans histiocytosis with frequent systemic involvement. The disease has widespread manifestation along with variable severity. Perirenal involvement was reported in 68 percent of patients with the disease. The disease is common among middle-aged men and is not inherited. However, few pediatric cases were reported.
What Is the Pathology of Erdheim-Chester Disease?
Erdheim-Chester disease is a lipo granulomatous disorder with infiltration from lipid-laden histiocytes, Touton giant cells (multinucleated giant cells present in areas with high lipid content), and varying fibrosis. Langerhans cell histiocytosis and Erdheim-Chester disease can co-exist and form 12 percent of cases.
Recently, V600E (valine replaced by glutamic acid at amino acid 600) BRAF (proto-oncogene) mutation was present in 54 percent of patients, raising the doubt for neoplastic origin. Since the BRAF gene is associated with the development of various cancers, the Erdheim-Chester disease has been classified as malignant. Inflammation also has a role in disease pathogenesis as increased levels of alpha interferon and interleukins are present.
What Are the Symptoms of Erdheim-Chester Disease?
The symptoms of the disease can be varied, but few known presentations are:
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Osteosclerosis (abnormal hardening of bone) of the long bone causing bone pain is the most common clinical symptom.
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Retroperitoneum involvement is associated with renal failure or renovascular hypertension.
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Neurological deficits.
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Multiorgan failure.
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Retroperitoneal fibrosis.
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Central nervous system involvement results in exophthalmos (protrusion of eyeballs from the socket), diabetes insipidus (a condition caused by an imbalance of water in the body), headache, ataxia (impaired coordination), and seizure.
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Dyspnea (shortness of breath).
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Cardiac involvement includes pericardial effusions, heart failure, and valvular disease.
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Pulmonary involvement.
What Are the Radiographic Findings in Erdheim-Chester Disease?
Skeletal Involvement
The features are:
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Metaphyseal and diaphyseal sclerosis bilaterally.
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Increase in symmetric lower limb uptake of Tc-bone scintigraphy.
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Cortical thickening.
Visceral Involvement:
1. Lung
- Pulmonary involvement is reported in 43 % of cases.
- Septal thickening and preserved lung volume.
- Chest radiographs show interstitial edema, pleural effusion, and cardiomegaly that do not respond to diuretics.
2. Orbital Tissue
- Optic nerve edema.
- Retrobulbar mass that causes proptosis (bulging eyes) and motility impairment.
- Expansion of the disease from the optic nerve to the hypothalamus could result in brain involvement.
3. Cardiac Involvement
- Occurs in 75 percent of patients with the disease and are frequently asymptomatic and are diagnosed incidentally through radiography.
- Circumferential soft-tissue sheathing of the thoracic and abdominal aorta and its branches.
- Pericardial infiltration is a common feature.
4. Intracranial Involvement
Involvement of the central nervous system is suggestive of poor prognosis.
5. Meninges
- Infiltration within the dural may mimic meningiomas (tumors developing from meninges), enhancing soft tissue mass.
- T2 signals show the infiltrates as hypointense.
- Hypothalamus involvement is the most common. Radiologically, intraparenchymal masses appear non-specific.
- Pituitary infundibulum leads to diabetes insipidus.
What Is a Hairy Kidney?
The hairy kidney is a radiographic sign that occurs in Erdheim-Chester disease. The sign refers to a soft tissue ring of perirenal infiltration seen during cross-sectional imaging studies of the disorder. The appearance of a hairy kidney in radio imaging is the pathognomic feature of the disease. The hairy appearance is caused by the thickening of bridging perirenal septa (Kunin septa). Kunin septa are fibrous tissue bands extending between the renal capsule and perirenal fascia. In a CT (computed tomography) scan, kidneys appear hairy as the perirenal infiltrate creates an irregular renal border, which does not undergo after administering iodinated contrast. Therefore differentiating it from the kidney itself.
What Are the Other Disorders That Can Produce Similar Findings?
Other pathologic conditions that produce similar findings are:
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Retroperitoneal Fibrosis: It is a rare systemic disease characterized by the proliferation of fibrous tissue. Skeletal imaging helps with differential diagnosis, as retroperitoneal fibrosis does not show bone involvement.
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Perirenal Lymphoma: They exhibit symptoms similar to Erdheim-Chester disease. The renal lymphoma appears as multiple solitary lesions.
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Amyloidosis: Clinical presentations of both diseases are similar. Amyloidosis includes a group of disorders characterized by amyloid protein deposition in tissues and organs.
How Is Erdheim-Chester Disease Diagnosed?
The diagnosis of the disease is made histopathologically with biopsies of affected tissues. The tissues present lipid-laden and foamy histiocytes that are associated with fibrosis. The immunohistochemical stain is positive for CD68, which confirms the presence of histiocytes. However, the cells were negative for S100, which rules out Langerhans cell histiocytosis. Therefore, based on these findings, the presence of Erdheim-Chester disease is confirmed. Several radiological examinations are performed before confirmation with a biopsy. Whole-body scans are required to rule out any malignancies.
How Is Erdheim-Chester Disease Managed?
Treatment of Erdheim-Chester disease is mainly immunomodulatory. Steroids, chemotherapy, and radiotherapy have little effect, and the disease may progress. The first line of treatment includes alpha interferons and anti-cytokine-directed therapy. Individuals without BRAF mutation had a moderately favorable response to Cladribine, whereas patients with BRAF mutation responded to targeted therapy with Vemurafenib. Surgical or percutaneous intervention is needed for orbital, hydronephrosis (excess urine accumulation in the kidney), or meningeal involvement. After treatment, the disease is monitored with frequent radiological follow-ups. The doctors recommend thoracoabdominal CT (Computed Tomography), FDG-PET (Fluorodeoxyglucose), and MRI (magnetic resonance imaging) to learn about the extent of the disease and treatment response.
What Is the Prognosis For Erdheim-Chester Disease?
The degree of visceral involvement is an indicator of poor prognosis and is a strong predictor of mortality. The prognosis for the disease was poor before the introduction of interferon therapy. Pulmonary fibrosis and renal and cardiac failure were the most common causes of death. The symptoms of pericarditis (inflammation of the heart) and pleural effusion (excess fluid accumulation between lung and chest) improved after interferon therapy. The histological manifestation of perirenal and perivascular infiltration remained stable after multiple follow-ups.
Conclusion
Hairy kidney disease is one of the characteristic features of Erdheim-Chester disease. Since the disease is a heterogeneous condition with varying clinical presentation, hairy kidneys, and coated aorta can aid in diagnosis. There is insufficient knowledge about the disease due to its rarity. Therefore, the cause and pathology remain unknown. Currently, limited treatment methods are available for disease management.
