Annular atrophic plaques of the skin (Christianson's disease)

A 69-year-old Caucasian man presented to the Gainesville Veterans Administration Medical Center for evaluation of several asymptomatic enlarging lesions on the face and forearms that had been present for 10 to 15 years. They were initially small but had progressively enlarged, especially during the previous 5 years. He reported having sustained a concussive grenade blast injury of the left temple and right forearm during the Korean Conflict in 1951. The injured areas healed uneventfully in 2–3 weeks. The patient was otherwise healthy, and the review of systems was noncontributory. Laboratory work-up (complete blood count, chemical profile, erythrocyte sedimentation rate, rheumatoid factor, hepatitis profile, antinuclear antibodies, urinalysis, and chest X-ray) was within normal limits. Lyme antibody titers were negative. Physical examination revealed similar-appearing lesions located variously on both temples, left preauricular and infraauricular areas, and the right forearm (Fig. 1). The lesions were large (ranging from 4 to 12 cm in diameter), centrally atrophic patches with ivory-colored thickened edges, and had the distinct appearance of healed skin grafts. Blood vessels were easily seen through the atrophic skin. All lesions were located on sun-exposed areas (predominantly on the patient's left side). No similar lesions elsewhere on the body or skin graft donor sites were found. The patient was treated with doxycycline 100 mg by mouth twice a day for 21 days to no avail, Intralesional steroids and clobetasol propionate ointment under occlusion were used without any change in the lesions. At the submission of this paper, the lesions remain stable. Skin biopsies were taken from the edge and center of the lesions, Histologic examination (Fig. 2) of the center of a lesion showed a flattened epidermis without interface changes. Sclerosis of superficial and mid, but not deep, dermal collagen was present, particularly within the specialized connective tissue surrounding eccrine structures. A focus of lymphocytic inflammation with rare plasma cells and edema was present at the dermal-subcutaneous interface. Histologic examination of the edge of the lesion showed a flattened epidermis overlying a perivascular and periadnexal lymphohistiocytic inflammatory infiltrate. The papillary dermis was sclerotic centrally, and sclerosis was present around one eccrine unit. Increased interstitial mucin was noted. Direct immunofluorescence using antibodies to IgG, IgM, IgA, and C3 was negative, A silver stain for borrelia organisms was negative. Electron microscopy of a biopsy from the advancing border of a lesion revealed foci of complete cytoiysis of the basilar epidermis above an interrupted basal lamina (Fig, 3a). Cellular debris was evident even within the subajacent papillary dermis (Fig. 3b). Abundant colloid-like material associated with occasional 8–10-nm straight tubules was also present within the upper papillary dermis. A solitary lymphocyte lay closely apposed to a basilar keratinocyte having large cytoplasmic vacuoles. Electron microscopy of a biopsy from the center of the same lesion revealed a flattened basilar epidermis and focal reduplication and interruption of the basal lamina (Fig. 3c). Abundantly interspersed among the collagen bundles of the upper and lower papillary dermis were aggregates that appeared amorphous at low magnification. Upon higher magnification, however, the aggregates could be seen to be comprised of straight and wavy tubules embedded in a finely granular matrix (Fig. 3d). A dermal blood vessel was surrounded by several basal laminae, just outside of which were presumptive lymphocytes with cerebritorm nuclei and histiocytes. No dermal elastic fibers could be identified. Collagen fibrils appeared normal.     

Bullous poikilodermatitic amyloidosis of the skin with junctional bulla development in IgG light chain plasmacytoma of the lambda type. Histology, immunohistology and electron microscopy]

A 75-year-old patient presented with bullae, poilokilodermatic skin and nail dystrophy as signs of systemic amyloidosis 1 year before an IgG myeloma of the lambda type was diagnosed. The skin lesions appeared at mechanically irritated locations on the trunk and at the tensor sites of the extremities. Histology showed a subepidermal blister and necrotic keratinocytes in the epidermis. There were amyloid deposits in the papillary dermis perivascular, and in the deep dermis around eccrine glands and in arrectores pilorum muscles. Polyclonal antibodies allowed classification of the deposits as amyloid composed of lambda light-chain immunoglobulins. Electron microscopy revealed globoid deposits of non-branching filaments typical of amyloid. The blister was formed at the level of the lamina lucida, with the lamina densa at the base of the bottom of the bulla. So far, junctional blister formation in bullous amyloidosis of the skin has been described only once. Our case is the second report of this blister type, and to our knowledge the first published report of a junctional blister in myeloma-associated systemic amyloidosis.     

Keratinocytes can differentiate into eccrine sweat ducts in vitro: involvement of epidermal growth factor and fetal bovine serum

BACKGROUND: in addition to formation of an epidermal sheet and dermal substitution, reconstruction of skin that possesses functionality is an important goal for dermatologists. OBJECTIVE: we attempted to regenerate eccrine sweat glands in vitro. METHODS: we constructed skin equivalent models with various combination of normal human keratinocytes and fibroblasts and also examined the effect of various growth factors. RESULTS: we found that keratinocytes invaded the collagen gels and formed eccrine duct-like structures, only when (i) the culture media contained at least 15 ng/ml of epidermal growth factor (EGF) and fetal bovine serum (FBS), (ii) the keratinocytes were derived from young donors, and (iii) fibroblasts were present in the gel. Interestingly, when cultured under the same conditions eccrine gland duct cells were unable to invade the gel. Immunohistochemical analyses revealed induction of carcinoembryonic antigen by EGF at the inner part of the eccrine duct-like structures. Proliferating cell nuclear antigen was expressed mainly in basal layers of the epithelia but was not observed in the deeply invaded part. Cytokeratin profiles of the reconstructed epithelia were consistent with those of the regenerating epidermis and partly with the eccrine sweat duct. CONCLUSIONS: although not perfect model, these results indicate that 'young' keratinocytes could differentiate into/toward eccrine sweat ducts in vitro in the presence of EGF and FBS in cooperation with dermal fibroblasts.     

Intra-epidermal retention of type VII collagen in a patient with recessive dystrophic epidermolysis bullosa

An infant born with severe blisters on the limbs, face, trunk, and oral mucosa was diagnosed by light and electron microscopy to have recessive dystrophic epidermolysis bullosa. Transmission electron microscopy showed that the basal lamina remained with the epidermis and that the floor of the blister was exposed collagen of the papillary dermis. No banded anchoring fibrils were observed along either the roof or the floor of the blister; however, small filamentous structures, possibly immature anchoring fibrils, extended down from the lamina densa along the blister roof. Some basal and suprabasal keratinocytes contained large vesicles filled with filamentous matrix of variable electron density. Immunofluorescent staining of skin for type VII collagen showed sparse and irregular staining of type VII collagen along the blister roof, and intense intracellular labeling for type VII collagen in clusters of epidermal cells in basal and suprabasal layers. Type VII collagen appeared to be synthesized by keratinocytes but not secreted.     

Epidermis reconstructed from the outer root sheath of human hair follicle. Effect of retinoic acid

In the present paper, we show that a multilayered and well-differentiated epidermis can easily and rapidly be generated in vitro from the outer root sheath of human hair follicles deposited on de-epidermized demis. Histologically, this epidermis presented characteristic features of normal human epidermis in vivo. Moreover, markers specific for interfollicular keratinocyte terminal differentiation, such as the K10 keratin, involucrin, membrane-bound transglutaminase, filaggrin and loricrin, were expressed in the reconstructed tissue. By in situ hybridization, keratin K5 and K10 mRNAs were detected in the basal and suprabasal cells, respectively, as in normal human epidermis. The differentiation pattern achieved in this reconstructed epidermis confirms the already reported phenotypical shift from outer root sheath cells to interfollicular keratinocytes and shows that this transition takes place in the absence of living fibroblasts. The differentiation of the reconstructed epidermis thus obtained was modulated by retinoic acid in a dose-dependent manner. This culture system on dead dermis is easier to handle than similar cultures on collagen-fibroblast lattices because of the resistance of dermis to mechanical forces and to collagenolysis. It could represent a valuable wound-healing model and a promising tool for pharmacological studies on in vitro reconstructed skin.     

Basement membrane components and galactosylhydroxylysyl glucosyltransferase in suction blisters of human skin

Basement membrane components and collagen biosynthesis were studied in suction blisters in human skin. The basement membrane components were characterized by immunofluorescence using specific antibodies to type IV collagen, laminin and fibronectin, and collagen biosynthesis was studied by assaying galactosylhydroxylysyl glucosylatransferase. In suction blisters, the separation of epidermis and dermis occurred above the lamina lucida, indicating that the basement membrane, composed of lamina lucida and lamina densa, forms a mechanically strong entity. During the regeneration phase of blisters, type Iv collagen and laminin were not observed in the old epidermal blister roof. This indicates that keratinocytes when separated from the underlying basement membrane or connective tissue do not synthesize laminin or type IV collagen. Galactosylhydroxylysyl glucosyltransferase activity could be demonstrated in blister fluid and was about the same as in serum when expressed on the basis of protein in fresh blisters. It increased by 2-3 fold during the repair of blisters, indicating that there was local production of this enzyme. Further studies revealed that pure epidermis contained galactosylyhdroxylysyl glucosyltransferase and hydroxyprolineand this suggests that epidermis may synthesize some collagen type which, according to these studies, is not type IV (basement memebrane) collagen.     

Microcystic adnexal carcinoma--a light and electron microscopic studies

Microcystic adnexal carcinoma (MAC) in a 48-year-old Japanese male was studied. A firm nodule had appeared on the right side of his upper lip at the age of 38 years and then had gradually enlarged. Light microscopic examinations revealed numerous strands and islands of basaloid cells and keratinous cysts with desmoplastic stroma in the dermis and subcutaneous tissue. Some keratinous cysts showed early calcification and some contained pilar structures. Clear cells resembling sebaceous gland cells were observed in the strands of tumor cells connecting the keratinous cysts. In the middle dermis, there were small ductal structures containing amorphous eosinophilic material. Immunoperoxidase staining for carcinoembryonic antigen was focally positive in the lumina of small ducts, on the ductal lining surface of tumor cells, and in the contents of keratinous cysts. Electron microscopic examinations revealed tumor cells resembling non-keratotic keratinocytes, and containing tonofilaments, mitochondria, and vacuoles. In some parts, tumors were differentiated to various types of sebaceous gland, sweat duct, or sweat secretary segments. Sebaceous gland cells contained lipid droplets and glycogen. Tumors differentiated to sweat duct had a marked similarity to embryo eccrine duct in the lower epidermis because of the presence of multivesicular dense bodies and periluminal filamentous zones and the absence of myoepithelial cells. Tumors differentiated to sweat secretary segments had a similarity to embryo eccrine secretary segments because of the absence of multivesicular dense bodies, periluminal filamentous zones and myoepithelial cells.     

Papillary Eccrine Adenoma with a Pomegranate-like Appearance

Papillary eccrine adenoma (PEA) is a rare cutaneous tumor which histopathologically presents numerous intradermal tubular structures with inward papillary projections. Only a few cases of PEA have been reported recently. We report a case of PEA of a 58-year-old Japanese man. The marked hyperkeratosis and pits gave the tumor the clinical appearance of a burst-open pomegranate. Compact hyperkeratosis within proliferated epidermis contained spiral ducts mimicking intraepidermal eccrine sweat ducts histopathologically. These keratinous structures were thought to correspond to the pores. Several tubular structures running up to the overlying thickened epidermis were observed in the upper dermis. With these findings and with immunohistochemical studies, we proposed that this tumor originated from eccrine sweat ducts.     

Human papillomavirus-associated plantar epidermoid cyst related to epidermoid metaplasia of the eccrine duct epithelium: a combined histological, immunohistochemical, DNA-DNA in situ hybridization and three-dimensional reconstruction analysis

BACKGROUND: We recently proposed that certain palmoplantar epidermoid cysts may be related to eccrine ducts and that human papillomavirus (HPV) 60 may play a role in their pathomechanism. However, the origin of palmoplantar epidermoid cysts is still controversial. OBJECTIVES: To examine the contribution of eccrine ducts and HPV 60 in the development of epidermoid cysts. METHODS: Five epidermoid cysts and four ridged warts that had developed on the soles of a patient were studied histologically, immunohistochemically and by DNA-DNA in situ hybridization. Using serial sections obtained from its entire body, a three-dimensional reconstruction (3DR) analysis was performed on the smallest cyst to analyse the relationship between the epidermoid cyst, eccrine duct and the overlying epidermis. RESULTS: Histological and DNA-DNA in situ hybridization analyses demonstrated both homogeneous intracytoplasmic inclusion bodies pathognomonic for HPV 60 infection and HPV 60 DNA sequences not only in all of the epidermoid cysts and ridged warts but also in the acrosyringeal portion of an eccrine duct, with the dermal portion of which the smallest cyst had been revealed to connect by 3DR analysis. However, immunohistochemical analyses using antibodies against human carcinoembryonic antigen (CEA), involucrin and several cytokeratins (CKs) revealed that the immunoreactivity of the cyst was not identical to that of the eccrine dermal duct but was identical to that of suprabasal layers of the epidermis. CONCLUSIONS: It was clearly demonstrated that an HPV 60-associated epidermoid cyst with immunoreactivities for CEA, involucrin and CKs which were identical to those of the epidermis connected with the eccrine dermal duct, supporting the idea that certain palmoplantar epidermoid cysts may develop following the epidermoid metaplasia of eccrine ducts with HPV 60 infection.     

Reconstitution of structure and cell function in human skin grafts derived from cryopreserved allogeneic dermis and autologous cultured keratinocytes

Grafts of allogeneic dermis plus autologous epidermal cell cultures were used to replace extensively burned skin. Cryopreserved split-thickness cadaveric skin was grafted onto debrided burn wound, and autologous keratinocytes were cultured from uninjured donor sites. Several weeks later, allograft epidermis was abraded and replaced with the keratinocyte cultures. The final grafts were thus composites of autologous cultured epidermis and allogeneic dermis. In a case with 28 months follow-up, reconstitution of the dermal-epidermal (BMZ.1) and microvascular (BMZ.2) basement membrane zones was studied immunohistochemically and ultrastructurally. Immediately before grafting, thawed cryopreserved skin reacted with antibodies against laminin and type IV collagen in normal patterns. Twenty-nine days after grafting, BMZ.1 reacted weakly with both antibodies, and anticollagen type IV reactivity was absent from BMZ.2. Antilaminin reactivity of BMZ.2, however, was moderately intense, consistent with recent neovascularization. On day 29, the allograft epidermis was replaced with autologous keratinocyte cultures. Twenty-five days later (54 d after allografting), staining of both BMZs was intense with both antibodies. Ultrastructurally, at day 76 (47 d after culture placement) BMZ.1 revealed only small hemidesmosomes, few incipient anchoring fibrils, and a discontinuous lamina densa. BMZ.2, however, was fully reconstituted. By 124 d, both BMZs appeared normal. Observations in the dermis at 76 d included the presence of lymphocytes, organellar debris, and hyperactive collagen fibrillogenesis, all indicative of dermal remodelling. The microvasculature was well differentiated, but no elastic fibers or nerves were found. In the epidermis, melanocytes and evidence of melanosome transfer were seen at 5, 47, and 95 d after grafting of keratinocyte cultures. We conclude that the composite procedure reconstitutes skin with excellent textural and histologic qualities.     

Distribution of major histocompatibility antigens in normal skin

The distribution of major histocompatibility antigens HLA-A,B,C (HLA), beta 2-microglobulin (beta 2m), and Ia-like antigens (HLA-DR; Ia) in normal skin was studied in frozen tissue sections by a four-step immunoperoxidase method and an avidin-biotin method employing monoclonal antibodies. HLA and beta 2m were present on the basal and spinous keratinocytes of the epidermis, on the outer root sheath epithelium in the infundibulum of the hair follicle, and on the excretory sebaceous duct epithelium. Ia-positive dendritic cells were found in the epidermis and hair follicles, but they were more frequent in the infundibulum and isthmus of the hair follicle than in its inferior portion or in the epidermis. In the straight eccrine duct, HLA and beta 2m-positivity was most striking in its lower portion. In the superficial duct, there was a less intense staining using the four-step procedure, but when an avidin-biotin method was used, the difference was less apparent. In contrast, the acrosyringial epithelium was markedly Ia-positive with decreasing intensity of staining as the duct penetrated the dermis. No HLA or Ia antigens were identified in eccrine glands and apocrine glands. Eccrine glands were slightly beta 2m-positive. HLA and beta 2m were uniformly present in non-dilated and dilated intradermal apocrine ducts.     

A 4.2 kb upstream region of the human corneodesmosin gene directs site-specific expression in hair follicles and hyperkeratotic epidermis of transgenic mice

Corneodesmosin (CDSN) is a desmosomal protein expressed in the epidermis during the late stages of differentiation and in the inner root sheath of hair follicles. The homophilic adhesive properties of the protein suggest that it reinforces keratinocyte cohesion in the upper layers of the epidermis (stratum granulosum and stratum corneum). In this study, we analyzed the expression of the CDSN gene in 16 human tissues. We confirmed the closely restricted expression pattern of CSDN. Indeed, apart from the skin, the mRNA was significantly detected only in the placenta and the thymus. As a step in elucidating the mechanisms of tissue-specific expression, transgenic mice bearing a 4.2 kb fragment of the human CSDN gene promoter linked to the LacZ gene were generated. The reporter-gene expression was detected in special areas of the inner root sheath of the hair follicles and the hair medulla but not in the epidermis. Induction of epidermis hyperproliferation however either by pharmacological agents or by wounding led to strong expression of the reporter gene in the keratinocytes of the stratum granulosum and the parakeratotic corneocytes of the stratum corneum. The data suggest that the genomic sequences and/or regulating factors responsible for the cell-specific expression of the human CDSN gene in the normal hair follicle as well as in the hyperproliferative epidermis are different from those necessary for expression in the normal epidermis.     

Presence of basal lamina-like substance with anchoring fibrils within the amyloid deposits of primary localized cutaneous amyloidosis

The dermal-epidermal (DE) junction areas of skin specimens obtained from 16 patients with either lichen amyloidosis or macular amyloidosis were studied. In the dermal papillae where amyloid was deposited, elastic fibers frequently were absent, but periodic acid-Schiff reaction after diastase digestion was homogenously positive. Ultrastructural studies revealed that a basal lamina-like substance with anchoring fibrils was present between and within amyloid deposits. By indirect immunofluorescence technique using an anti-basement membrane zone antiserum obtained from a patient with bullous pemphigoid, specific linear fluorescence occurred at the DE junction, and in a reticular pattern in dermal papillae. It seemed that apoptotic keratinocytes of the epidermis brought down basal lamina and fine fibrous components attached to it when these cells dropped down to the papillary dermis and became the source of amyloid. These findings support the hypothesis that epidermal keratinocyte degeneration plays an important role in the histogenesis of cutaneous amyloidoses.     

Monoclonal Antibody OKB19, Reactive with a B-Lymphoid Differentiation Antigen (CD19), Binding to Basal Layer Keratinocytes of Normal Human Skin

Monoclonal antibody (moAB) OKB19 reacts with CD19 antigen, which is the broadest lineage-specific surface marker on B-lymphocytes. In frozen tissue sections, using an immunohistochemical technique, the OKB19-positive cells in the basal layer were sharply demarcated from the negative suprabasal layers. In normal hair follicles, the OKB19 reactivity was also confined to one layer of the dermal side of the outer root sheath. However, this reactivity gradually disappeared in the lower areas. The inner surface of the lumina in the eccrine duct was weakly stained with OKB19. The basal keratinocytes were also stained with OKB19 in the lesional epidermis of the various dermatoses examined in this study, when the basal keratinocytes remained unaffected. Even in the hyperproliferative state of psoriasis, the OKB19 reactivity was confined to the basal layer. Several kinds of tumor cells derived from the skin were not stained with OKB19. No labeling was seen even in the basaloid cells of basal cell carcinoma, which are morphologically similar to basal keratinocytes. B4 and Leu-12, other monoclonal antibodies reacting with CD19, did not recognize any keratinocytes in the normal human skin. MoAB OKB19, therefore, reacts with an antigen present on basal keratinocytes and provides a probe for the isolation of the basal keratinocyte subpopulation. Thus, this antibody should be useful in studies of not only B-lymphocyte differentiation, but also normal and aberrant differentiation of the epidermal keratinocytes.     

Papillary eccrine adenoma: an electron microscopic study

A case of papillary eccrine adenoma was studied by electron microscopy. Dilated ducts that contained granular eosinophilic material, often associated with intraluminal papillary projections were observed. The ductlike structures were composed of basal and luminal cells. Within the luminal cells there were intracytoplasmic cavities, but neither secretory granules nor glandular structure were observed. On the basis of our observations, papillary eccrine adenoma appears to differentiate toward ductal structures of the eccrine sweat apparatus.     

In vitro reconstitution of skin: fibroblasts facilitate keratinocyte growth and differentiation on acellular reticular dermis.

Extensive full-thickness burns require replacement of both epidermis and dermis. We have described a method in which allogeneic dermis from engrafted cryopreserved cadaver skin was combined with cultured autologous keratinocytes. In the present study we combined human keratinocytes and fibroblasts, and acellular human dermis in vitro and transplanted this "reconstituted skin" into athymic mice. Both human papillary dermis in which the basement membrane zone has been retained and human reticular dermis that has been repopulated with human dermal fibroblasts are good substrates for keratinocyte attachment, stratification, growth, and differentiation. Both of these dermal preparations can be lyophilized and stored at room temperature without losing their ability to support keratinocyte growth. In contrast, human papillary dermis that has been treated with trypsin lacks laminin and collagen type IV in the BMZ and supports keratinocyte attachment and differentiation less well.     

Transient bullous dermolysis of the newborn

A case of transient bullous dermolysis of the newborn is reported. A healthy Hispanic newborn developed bullae during the first two days of life. From age two to four weeks, the lesions healed with milia formation. There was no residual scarring or hypopigmentation. An induced blister showed dermal-epidermal separation with the PAS-positive basement membrane in the epidermal roof. PAS-positive inclusions were present in the cytoplasm of a few basal cells. Examination by electron microscopy showed degeneration of the collagen and anchoring fibrils. There were numerous stellate inclusions in the endoplasmic reticulum of the cytoplasm of the lesional basal keratinocytes.     

Eccrine tubular adenoma--a histopathological, histochemical, and ultrastructural study

A case of eccrine tubular adenoma on the dorsum of the right foot is presented. Histopathologically, in the central nodule of the tumor, the whole dermis was involved and the tumor islands were connected to the epidermis; in the rest of the lesion, tumor islands were observed in the upper dermis. The tumor islands were composed of cystic or alveolar structures and cell masses possessing multiple lumina. Tubules were surrounded by two or more layers of epithelium forming papillations projecting into the lumen. There were only a few basaloid islands and no sclerotic strands. The tumor cells were well differentiated. Acid mucopolysaccharides were seen in the stroma. Histochemically, phosphorylase and acid phosphatase reacted moderately. Succinic dehydrogenase gave a weak reaction and β-glucuronidase was negative in tumor cells. Ultrastructurally, intracellular ducts with numerous microvilli, periluminal filamentous zones, and many multivesicular dense bodies surrounded by a limiting membrane were observed. Keratohyalin granules were absent. Based on these findings, the tumor reported here was considered to be an adenoma differentiating toward the eccrine duct. Some aspects resembled tubular apocrine adenoma, syringoma and basal cell tumor with eccrine differentiation, but they were most similar to papillary eccrine adenoma.     

INTRAEPIDERMAL FREE NERVE ENDINGS RELATING TO EPIDERMAL MELANOCYTES IN SPOTTED GUINEA PIGS

Intraepidermal free nerve endings were studied in spotted (black and white) guinea pigs. Specimens were obtained from black, gray, and white areas. Twenty blocks were made from each area and sections were examined by electron microscopy. Intraepidermal free nerve endings were found in the interfollicular epidermis of all three areas. The distribution density for the black areas was about twice that for the white areas. The frequency in the gray areas was intermediate between that for the black areas and that for the white areas. Intraepidermal free nerve endings contacted the melanocytes directly in the interspaces between the basal lamina of the epidermis and the cytomembrane of the melanocyte or the dendrite of the melanocyte in the intercellular spaces between basal keratinocytes. In most cases, their axons were ensheathed by Schwann cells. In some cases, a part of the axon expanded like a balloon about 200–300 nm in diameter. The ballooning structure contained several vacuoles about 40–60 nm in diameter. These vacuoles seemed to have been secreted into the extracellular spaces. In such cases, an accumulation of dense materials was observed along the opposed membrane of the vacuole and the cytomembrane of the melanocyte. In other cases, the cytomembranes of axons and those of melanocytes seemed to form synapse-like structures.     

Sweat duct milia – immunohistological analysis of structure and three-dimensional reconstruction

The fine structure of sweat duct milia and the pathomechanism in their aetiology are still unknown. To examine the relationship and connection of milia to the sweat ducts as well as to the overlying epidermis, nine sweat duct milia, six incomplete and three complete, were studied by three-dimensional reconstruction (3DR) analysis based on photomicrographs obtained after histological and immunohistochemical staining with antibodies against carcinoembryonic antigen (CEA), cancer antigen (CA 50) and human cytokeratin 19 (CK 19). In both incomplete and complete milia, an eccrine duct expressing the antigens penetrated into the cyst wall at the centre of its base, formed a circular path within the wall, and opened into the inner cavity. The eccrine duct was mature in eight milia and immature in one. In the cyst wall, CA 50 and CK 19 were detected throughout the entire cyst except for the most apical portion of incomplete milia, where the cyst wall fused with the overlying epidermis which did not express any of the antigens. CEA was distributed mainly in the basal half of the milia. The finding that the path of the eccrine duct within the cyst wall is circular conflicts with the currently accepted concept of simple penetration of the eccrine duct into the wall, suggesting an acrosyringeal origin of the milia. An incomplete milium is the result of fusion between cells derived from an eccrine duct and those derived from the surrounding epidermis, while the formation of a complete milium does not involve this fusion. Received: 10 November 1994