MON-511 Erdheim-Chester Disease: A Challenging Diagnosis in a Patient with Ataxia, Osteosclerotic Bone Lesions, and a Long-Standing History of Central Diabetes Insipidus

Abstract

Background: Erdheim- Chester Disease (ECD) is a rare hematopoietic neoplasm characterized by multi-organ infiltration with CD-68 -positive, CD1a-/S100-negative foamy histiocytes causing xantho-granulomatous inflammation. ECD most commonly involves the skeleton. CNS, pulmonary and CV involvement are also reported. Clinical Case: A 47-year-old male with a prior history of central Diabetes Insipidus (DI) presented with bone pain and ataxia. He was initially referred in 1993 for evaluation of DI. It was concluded that he had lymphocytic infundibulitis (LI), based on the finding of a thickened pituitary stalk on MRI while CSF revealed no evidence of infection or neoplasm. His DI was controlled with DDAVP. He had no other anterior pituitary hormone deficiencies. Although subsequent MRI showed resolution of the pituitary stalk thickening, his DI persisted. In 2012, he developed progressive gait instability, slurred speech and impaired motor coordination. On exam, he exhibited horizontal nystagmus, dysarthria, and truncal ataxia greater than limb ataxia. A brain MRI revealed absence of the posterior pituitary bright spot, enhancement along the proximal 7th and 8th nerve complex, disproportionate cerebellar atrophy and enhancement along the bilateral cerebellar folia. He complained of progressive, chronic leg pain since 2005. In 2018, he underwent tibial bone biopsy for an osteosclerotic lesion with diagnosis of Paget’s disease (PD). His Ca, Phos, 25OH- D, PTH, and Alk Phos were normal. Subsequent X-rays noted lesions of the pedicle of the left shoulder and pelvis, medullary sclerosis in the humeral diaphysis, and symmetrical lesions in the distal femur and tibia, bilaterally. Bone scan and FDG-Pet scan showed increased activity in the lesions. A repeat tibial biopsy revealed the marrow was infiltrated with histiocytes, fibrosis and sclerosis of trabecular bone. The histiocytes were highlighted by CD163, CD68, CD14, factor XIIIa and fascin A few scattered histiocytes were BRAF V600E immuno-stain positive, consistent with a diagnosis of ECD. His symptoms improved on Vemurafenib. Conclusion: We report a male with ECD who initially presented with isolated DI and a clinical course that mimicked LI. DI is a feature that occurs early in the disease process in 25% of patients. More than 10 years later, he developed ataxia and multifocal osteosclerotic bone lesions. His bone lesions were misdiagnosed as PD, but a repeat bone biopsy led to the correct diagnosis. In contrast to PD, the bone lesions in ECD are bilateral and symmetric and affect the diaphysis of long bones, specifically. As in our case, some patients with ECD can be asymptomatic for decades. For symptomatic patients who are BRAFV600E +, the B-Raf enzyme inhibitor, Vemurafenib, is recommended. His diagnosis was challenging, because ECD is rare (500 cases) and has features that overlap with other more common medical conditions.