Discussion
Histiocytosis is mainly manifested by bone involvement, but extra-osseous manifestations in 50% of cases are also present.(12, 13) Kidney involvement pattern, reported in 63% of these patients, was in the form of hairy kidneys with peri-renal fat infiltration (also reported in our patient). Moreover, retro-peritoneal fibrosis was also confirmed in 30% of the patients. (4, 14)
Cardiac manifestations include epicardial fat involvement and soft tissue infiltration in the right AV groove area, causing RCA encasement. In some cases, epicardial involvement causes a mass with a pressure effect on its’ underlying cavity (RA and RV free wall). (15) Pericardial involvement manifests as increased pericardial thickness, effusion, and even tamponade.(8) Other cardiac complications include rhythm disorders, conduction abnormalities, and valve involvement.(16)
Extra-cardiac manifestation in the form of peri-aortic infiltration, known as the coated aorta, is reported as soft tissue infiltration at the level of the aortic arch, sometimes affecting the coronary arteries, leading to MI.(12) (7)
However, cardiac involvement is mainly in the form of an RA pseudo-tumor and infiltration of the right AV sulcus. (15) The cause of cardiac pseudo-tumor, mainly associated with BRAF mutation, is still unclear. However, RA includes cardiac appendage stem cells that originate from medullary progenitors, so the stages of somatic mutation can occur during their evolution.(4) By examining the BRAF gene in these patients, those with this mutation had more cardiac band CNS involvement.(4, 17) Our patient had SLC29A3 mutation, which was previously seen in histiocyte-lymphadenopathy plus syndrome, including Faisalabad histiocytosis, H-syndrome, pigmented hypertrichotic dermatosis and insulin-dependent diabetes.(19)
ECD patients’ pathology shows bland xantho-granulomatous inflammation with different degrees of fibrosis and foamy, lipid-laden histiocytes.(18)
Cardiac MRI of the patients shows soft tissue mass density appearing Hypo-intense in the balanced steady-state free precession (B-SSFP) and T2W sequences. In addition, slight diffuse hyper-intensity is seen in fat signal suppression. In the T1W sequence, late enhancement of soft tissue lesions is seen in favor of disease activity and inflammation, as was the case with our patient’s MRI.(8)
Treatment with vemurafenib for ECD patients with the BRAF V600F mutation is recommended, but in other motations, as in our patient, treatment with Interferon-alpha and corticosteroids and non-specific therapies are used, and localized treatments such as radiotherapy treatment also have a limited role in treating the disease and its local complications.(20-22)