At 6-week follow-up after the intralesional steroid injection, the patient’s pain continued to abate, and she was ambulating with crutches. Repeat CT scan of the right distal femur showed improvement of the extraosseous soft-tissue component, while the lucency in the femur itself remained unchanged. The decision was made to proceed with a second intralesional corticosteroid injection under CT guidance. The patient’s symptoms continued to improve, and repeat imaging 1 year after her steroid injections showed substantial bony healing with reconstitution of her cortical bone (Figures 10A-10E).
The patient had had 4 distinct tumors consistent with EG and was referred to a medical oncologist for further workup. The patient began treatment with zoledronic acid to prevent development of further lesions. At most recent follow-up, the patient was 18 months out from her second intralesional corticosteroid injection and was doing very well. She reported being pain-free and was walking 3 to 4 miles per week without gait aids. There was no evidence of new disease. The medial distal femur lesion was completely healed, and the distal metaphyseal lesion was nearly healed, with very little residual evidence of lesions.
Discussion
Adult-onset multifocal EG is a rare entity. Most affected patients develop lesions in the axial skeleton, with the skull, mandible, and vertebrae most commonly involved.14 Only 5 cases of femoral EG have been reported, one of which was multifocal.11,14-17
Of these patients, 3 were between the ages of 33 and 53 years and had insidious onset of hip pain that failed conservative management.14,15,17 Further imaging and biopsy revealed unifocal EG in the proximal femur in each case. Each patient received a different form of treatment, including curettage and radiation, radiofrequency ablation, and/or physical therapy. At the time of publication, all patients had reported improvement in their clinical symptoms.14,15,17 The fourth patient was a man with human immunodeficiency virus (HIV) with 3 months of progressive thigh pain. Further evaluation found an isolated EG of the femoral diaphysis that progressed to pathologic fracture. He was treated with curettage and intramedullary nailing, and had improved symptoms and radiographic signs of healing at 30-month follow-up.16
An interesting case by Kerzl and colleagues11 reported a 63-year-old woman with a 24-year history of multiple symmetric lesions of the femora, leading to multiple pathologic fractures. Like our patient, her initial lesion was in the skull. Initial pathology specimens led to the diagnosis of EG. However, as the patient aged, she developed symptoms of diabetes insipidus and xanthelasma, which led to reevaluation of histology from 3 bony lesions. The patient was determined to have multifocal EG of the skull and femur, with simultaneous occurrence of Erdheim-Chester disease, which also causes bone lesions in addition to diabetes insipidus and xanthelasma.11
Though LCH was initially described more than 50 years ago, many aspects of LCH remain an enigma, especially in adults. The etiology of the disease is poorly understood. Controversy exists regarding whether LCH is primarily an immunoregulatory, neoplastic, or reactive disorder. The vast majority of adult cases described in the literature are EG, with very few cases of multisystem disseminated disease reported.5
The spectrum of disorders constituting LCH is heterogenous. Eosinophilic granuloma is the most common form, reportedly accounting for 60% to 70% of all cases, usually presenting as solitary bone lesions.6 Eosinophilic granuloma refers to the localized form of LCH, in which the disease is limited to bone or lung.18 This is the least aggressive form of the disease, with the most favorable prognosis. Hand- Schüller-Christian disease is a chronic, recurring form of LCH, with disseminated disease, affecting both bone and extraskeletal sites. Hand-Schüller-Christian disease is known for the classic triad of diabetes insipidus, exophthalmos, and destructive bone lesions. Patients may also present with otitis media or neurologic complaints from pathologic vertebral fractures. Letterer-Siwe disease refers to the acute, disseminated, fulminant form of LCH. This is the least common form of LCH and is predominately described in young children. Patients present with hepatosplenomegaly, lymphadenopathy, skin rash, fever, anemia, and thrombocytopenia.19 It is rapidly progressive, leading to multiorgan dysfunction and death within 1 to 2 years.18
The classification of LCH follows the Histiocyte Society guidelines developed from multicenter randomized trials in children.3 Classification is based on affected organs and is divided into 2 categories: single-system disease or multisystem disease. Single-system disease may be single site (bone, skin, or solitary lymph node) or multisite (multifocal bone disease or multiple lymph nodes). Multisystem disease is further classified into low-risk or risk groups. The low-risk group involves disseminated disease without involvement of risk organs (lungs, liver, spleen, and hematopoietic system). Involvement of 1 or more risk organs places the patient in the risk group, associated with the least favorable prognosis.3