Background Lipodystrophic syndromes are a heterogeneous group of genetic or acquired disorders characterized by a generalized or partial loss of body fat with severe metabolic complications linked to insulin resistance and dyslipidemia. Specific radiographic bone features have been described in isolated cases or small cohorts of patients.
Objectives To describe the bone imaging features of lipodystrophies in the largest cohort ever published.
Methods Twenty-four patients with lipodystrophic syndromes followed in our reference center with available bone imaging were studied. Twenty-two had genetic lipodystrophies (12/22 familial partial lipodystrophies (FPL, linked to mutations in LMNA encoding lamin A/C (n=9), PPARG encoding PPARg (n=2), or PLIN encoding perilipin (n=1)) and 10/22 congenital generalized lipodystrophies (AGPAT2-linked CGL1 (n=8) or CGL2 due to seipin mutations (n=2)). Two had acquired generalized lipodystrophies (AGL) in a context of non-specific autoimmune disorders. They were retrospectively reviewed in consensus by 2 senior musculo-skeletal radiologists, 3 rheumatologists and 1 endocrinologist. Standard bone X-rays were available for all of them with a radiographic follow-up for 2 of them. Four patients underwent magnetic resonance imaging (MRI) and two computed tomography (CT).
Results All FPL patients (n=12, 11 women, mean age 45 years (±14, SD) had non-specific radiographic abnormalities. In CGL patients (n=10, 7 women, mean age 30 years (±18, SD), we observed three types of radiographic alterations: 7 patients (6 CGL1 and 1 CGL2) had diffuse osteosclerosis, eight (7 CGL1 and 1 CGL2) had one or several well-characterized lytic bone lesions and 4 (4 CGL1) had pseudo-osteopoikilosis (figure). Lytic lesions usually involved the epiphysis as well as the metaphysis in the proximal (n=7) and distal femur (n=6), the proximal tibiae (n=6) and the distal humerus (n=6). Additionally, 5 patients, all with lytic lesions, had honeycomb multikystic lesions that appeared between age of 2 and 14 in one. In AGL, pseudo-osteopoikilosis was the sole bone abnormality observed in one of the 2 patients. MRI examination showed that lytic lesions were homogeneous with low T1 and high T2 signal. The 4 CGL patients who underwent a MRI had diffuse fatty bone marrow alterations with intermediate T1 and high T2 signal, notably in radiographically normal areas, as observed in anorexia, suggesting a serous transformation of bone marrow. Only one CGL1 patient had a symptomatic lytic lesion, which resulted in a spontaneous knee fracture and subsequent secondary osteoarthritis.
Conclusions The most frequent imaging abnormalities seen in generalized lipodystrophic syndromes are diffuse osteosclerosis, lytic lesions and/or pseudo-osteopoikilosis. These bone abnormalities are more frequently associated with AGPAT 2 than seipin mutations. Diffuse MRI abnormalities in fatty bone marrow suggest that this fat tissue is disturbed. These features, the pathophysiology of which is poorly understood, may help clinicians for an early diagnosis in pauci-symptomatic patients.
Disclosure of Interest None declared