The study of the panniculitides has been traditionally considered as one of the most difficult subjects within the realm of inflammatory skin diseases. The reasons for this difficulty are varied. First of all, with few exceptions, most panniculitis exhibits the same clinical features, namely erythematous nodules on the lower legs, and this morphologic monotony is disappointing for clinicians who like to establish specific diagnosis on the basis of the clinical features of the skin disorders. Second, histopathologic reasons also contribute to the increasing pitfalls in the study of panniculitis because often biopsies are wrongly performed; the cutaneous specimens obtained are too superficial or too small and are sent to the laboratory with inaccurate clinicopathologic correlation. Clinicians should be aware that biopsies from panniculitis should be large enough, with surgical excision of the entire thickness of the involved subcutaneous fat; such biopsies should be obtained from early lesions, if possible from nodules that are discovered by palpation but are not yet visible, because after a few days or weeks of evolution, many panniculitic disorders, especially among lobular panniculitides, exhibit the same histopathologic features, namely lipophagic granuloma, and this is an entirely unspecific pattern that may be seen in different panniculitides. However, with adequate biopsy specimens from early lesions and correct clinicopathologic correlation, dermatopathologists can render specific diagnosis for each type of panniculitis, in the same way that they are able to do it for inflammatory skin disorders involving the epidermis or the dermis. For histopathologic diagnosis of panniculitis, the best special technique is to cut deeper sections, and dermatopathologists should study as many sections as they need to, attempting to render more than just a descriptive report, because if the specific diagnosis remains within the paraffin-embedded tissue due to an insufficient number of studied sections, the clinician receiving that report will be also disappointed and reluctant to perform new biopsies in future patients who have panniculitis. For these reasons, too many clinicians believe that biopsies of panniculitis serve only to leave large scars on the lower legs of women. It is the responsibility of the dermatopathologists to correct this mistake and render specific diagnoses in the language of clinical dermatology.
This issue describes the many aspects of the different entities that may be grouped as mostly lobular panniculitides, as a continuation of other reviews presenting mostly septal panniculitides that have been published elsewhere.1 The issue begins with a description of the anatomy and histology of normal subcutaneous fat, the different types of necrosis of adipocytes, and a proposal of classification of the panniculitides. Then a comprehensive clinico-pathologic overview of the most common lobular panniculitides is presented, with emphasis on the characteristic histopathologic features for specific diagnosis and a brief comment about the treatment for each entity. Because it is the most frequent type of panniculitis, erythema nodosum is also included here, although it is mostly a septal panniculitis. Finally, subcutaneous panniculitic-like T-cell lymphoma is not an inflammatory condition, but a neoplastic one due to monoclonal proliferation of cytotoxic T-cell lymphocytes, but it is included in the issue because it may simulate a lobular panniculitis both from clinical and histopathologic points of view.
This issue describes the many aspects of the different entities that may be grouped as mostly lobular panniculitides, as a continuation of other reviews presenting mostly septal panniculitides that have been published elsewhere.1 The issue begins with a description of the anatomy and histology of normal subcutaneous fat, the different types of necrosis of adipocytes, and a proposal of classification of the panniculitides. Then a comprehensive clinico-pathologic overview of the most common lobular panniculitides is presented, with emphasis on the characteristic histopathologic features for specific diagnosis and a brief comment about the treatment for each entity. Because it is the most frequent type of panniculitis, erythema nodosum is also included here, although it is mostly a septal panniculitis. Finally, subcutaneous panniculitic-like T-cell lymphoma is not an inflammatory condition, but a neoplastic one due to monoclonal proliferation of cytotoxic T-cell lymphocytes, but it is included in the issue because it may simulate a lobular panniculitis both from clinical and histopathologic points of view.