Background: Localized loss of adipose tissue without antecedent clinical or histologic inflammation is termed idiopathic lipoatrophy.
Objective: Our purpose was to study the clinical and pathologic features in 16 patients with clinically focal lipoatrophy and a distinct pathologic pattern of fat lobule involution.
Methods: A retrospective study of 16 patients was performed.
Results: The buttocks and proximal extremities were involved most frequently. Lesions were solitary in 10 patients and multiple in six. Nine patients had received intramuscular or intraarticular corticosteroid or antibiotic injections in the affected areas before the development of lipoatrophy. Histologic examination showed that individual fat cells were decreased in size and separated by hyaline material. Progressive reduction in the size and number of adipocytes resulted in diminutive fat lobules with prominent vessels resembling embryonic fat lobules. Some adipocyte masses were acidophilic. Scattered macrophages, confirmed by immunoperoxidase staining for CD68 (KP-1), were identified within the fat lobules and surrounding connective tissue. Yellow-gray granules were recognized within the cytoplasm of macrophages in nine cases. Macrophages becoming lipophages were observed by electron microscopy in one case. Other inflammatory cells were not prominent.
Conclusion: This is a common pattern of postinjury response to fat tissue characterized by macrophage infiltration of the fat lobules in variable numbers. The term involutional lipoatrophy is justified by the resemblance of the distinctive pathologic changes to embryonic fat lobules.