Skin imaging in the diagnosis of Kaposi sarcoma

Dear Editor,

Kaposi sarcoma (KS), a malignancy associated with human herpesvirus type 8 (HHV-8) infection, commonly involves immunocompromised individuals.¹ In recent years, non-invasive imaging techniques such as dermoscopy and reflectance confocal microscopy (RCM) have become crucial for diagnosing challenging dermatological conditions.^2,3 The combined use of dermoscopy and RCM for evaluating KS has not been reported.

A 72-year-old man presented with scattered purple nodules on the dorsal aspect of both feet, since last two years. The lesions began as two pea-sized, purplish-red papules on the left foot. Some lesions subsequently ulcerated and developed surface crusts, without any significant discomfort to the patient. Despite previous cryotherapy, the lesions persisted and gradually increased in number [Figure 1a]. Laboratory investigations, including complete blood count, liver and kidney function tests, syphilis serology, and HIV screening, were unremarkable. Dermoscopic examination (CBS-908, Bosch Electronics Co., Ltd., Taiwan, China, 50×, polarised) revealed localised scabs and scales, with rough surface texture. An uneven, structureless purple-blue to red background was observed, with locally visible brownish small spherical structures and linear vascular structures, along with short, tortuous vessels set against angiomatous or frankly haemorrhagic blotches [Figures 1b and 1c]. A characteristic “rainbow pattern” manifesting as irregularly distributed rainbow-like lustre was observed. Central ulceration and haemorrhagic crusting were noted in some lesions. No typical pigment network was identified . While the “rainbow pattern” has been reported as a dermoscopic feature of KS, it is not pathognomonic, also documented in lichen planus and melanoma.^4,5 RCM examination (VivaScope 1500, Lucid Inc., New York, USA) demonstrated fusiform and linear mass structures within the dermis [Figure 2a]. Dilated vessels appeared as enlarged black lumens. Perivascular inflammatory cell infiltration, extravasated red blood cells, and irregular substance deposition (possibly haemosiderin) were evident [Figures 2b, 2c]. The histopathological hallmarks of nodular KS include well-demarcated, interwoven bundles of spindle cells in the dermis, containing numerous irregular, slit-like vascular lumens, accompanied by red blood cell extravasation and haemosiderin deposition.⁶ Both the dermoscopic and RCM findings were consistent with classic nodular KS. Subsequent histological examination revealed spindle cell clusters arranged in interwoven bundles and plexiform distribution. Spindle cell masses contained numerous irregular, slit-like vascular lumens, with associated red blood cell extravasation, inflammatory cell infiltrate, and haemosiderin deposition [Figures 3a-c]. Immunohistochemistry was positive for endothelial cell markers CD34 and Factor VIII-related antigen (F VIII); HHV-8 was detected. The Ki-67 proliferation index was approximately 20%, indicating moderate tumour cell proliferation [Figures 3d-f]. Based on the clinical presentation, dermoscopic and RCM features, histopathology, and immunohistochemistry, the patient was diagnosed with classic nodular KS.

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Figure 1: Clinical image of kaposi sarcoma and dermoscopic features. (a) Multiple pea-sized papules and nodules on the dorsum of the left foot, exhibiting a purplish-red hue with overlying ulceration and scab formation in some lesions. (b) Dermoscopy revealed a uniform “rainbow pattern” with brown globules (green arrow) , scabs (red arrow) and scales (blue arrow). (c) Furthermore, visible linear vascular structures (white arrow), and short, tortuous vessels (black arrow) can be observed.

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Figure 2: Reflectance confocal microscopy characteristics of the lesion. (a) Fusiform and bundled mass structures are evident within the dermis. (b) Enlarged black lumens are visible, consistent with dilated vascular structures (red box). (c) Perivascular inflammatory cell infiltrate is present (white arrow). Extravasated red blood cells and deposits of irregular material (blue box) surround the vessels suggestive of haemosiderin.

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Figure 3: Histopathological features of the dorsal left foot lesion showing: (a) Bundles and clusters of intersecting fusiform/spindle cells (Haematoxylin and eosin, 100x). (b) Higher magnification reveals numerous irregular, fissure-like vascular lumina within the fusiform cell proliferation, accompanied by extravasated erythrocytes, inflammatory cell infiltrate, and haemosiderin deposition (Haematoxylin and eosin, 400x). Immunohistochemical features of the dorsal left foot lesion showing. (c) Ki-67 staining showing a proliferation index of approximately 20% (400x). (d) Positive staining for CD34 (400x), (e) Factor VIII positivity (400x), and (f) Positive staining for HHV-8 (400x).

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The clinical diagnosis of KS is challenging and often requires differentiation from conditions such as kaposi-like hemangioendothelioma, spindle cell hemangioma, moderately differentiated angiosarcoma, and papular angioplasia.⁷ The current diagnostic standard for KS i.e. a skin biopsy for histopathological confirmation with HHV-8 positivity on immunohistochemistry, is invasive and not always feasible. This poses a clinical challenge, necessitating the exploration and application of non-invasive diagnostic techniques.

In our case, the dark purple to brown macules and papules on the dorsal aspect of the patient’s left foot clinically resembled other pigmentary or vascular dermatoses. Characteristic dermoscopic features of KS include the “rainbow pattern” and polymorphous vascular structures. Dermoscopy in this patient revealed irregular rainbow pattern and polymorphous vascular structures against a purplish-blue to red background, consistent with literature.⁴ However, the “rainbow pattern” is not pathognomonic for KS on dermoscopy. Therefore, diagnosing KS based solely on dermoscopic findings remains controversial. RCM enables real-time, high-resolution visualisation from the epidermis into the reticular dermis. In this case, RCM examination of the lesion demonstrated proliferating spindle cells and the formation of abnormal vascular structures. These aberrant vessels were surrounded by scattered erythrocytes and inflammatory cell infiltrates, with peripheral haemosiderin deposits. The combined dermoscopic and RCM findings strongly suggested KS, which was subsequently confirmed by histopathological examination.

Corroborating findings from various modalities showed that the purplish-blue to red background and linear vascular structures observed dermoscopically corresponded to dilated, black lumen-like structures on RCM and to numerous irregular, dilated vascular channels within spindle cell clusters on histopathology. The dermoscopic rainbow pattern correlated with disordered spindle cell clusters in the dermis on RCM, which histopathologically manifested as intersecting bundles and clusters of spindle cells. The circular-to-oval irregular structures aggregated in the dermis on RCM corresponded histopathologically to scattered extravasated erythrocytes and perivascular haemosiderin deposits [Table 1].

This report demonstrates that the combined application of dermoscopy and RCM as imaging modalities may assist clinicians with a more comprehensive approach for diagnosing KS.