Nail involvement in Kaposi sarcoma: A rare location

Dear Editor,

Kaposi sarcoma (KS) is a tumour primarily seen on the skin. Basic lesions are macules that evolve into papules and then into red, bluish, or brown nodules. They can be single or multiple, with a smooth, keratotic, or ulcerated surface. These lesions frequently occur on the lower limbs, but generalised involvement is possible. Nail damage during KS is rarely described in the literature, particularly with onychoscopic features. We collected cases of KS between 2020 and 2024, in our department. The data collection process included a systematic evaluation of nail changes of all patients by clinical examination and dermoscopic examination when applicable.

Among those 28 patients who presented with cutaneous involvement, only 4 had nail involvement. None had isolated nail damage. The average patient age was 78 years. Skin involvement consisted of confluent angiomatous papules, nodules, and plaques, with a predilection for the feet and interdigital spaces and preceded nail involvement in all patients. The average time for the appearance of nail damage was 2.5 years. Three patients had involvement of the single big toe, and one patient, of two nails (the big and 2^nd toes). The clinical signs observed included nail dystrophy (2 cases), onycholysis (2 cases), sub-ungual hyperkeratosis (3 cases), purple-red areas (3 cases) erythematous-purplish plaque of the cuticle (1 case), and angiomatous papule of the proximal fold (1 case). Onychoscopy showed a rainbow pattern (2 cases), peri ungual erythema (2 cases), surface scales (2 cases), erythematous areas in the proximal nail plate (1 case), and red-purplish areas of the nail bed (1 case), cuticle (1 case), and the proximal fold (1 case). Dermoscopic findings have been summarised in Table 1 and depicted in Figures 1-3. A biopsy guided by clinical and dermoscopic examination was done in 2 patients. Histological analysis showed dermal vascular proliferation, vessels of variable size and shape with extravasation of red blood cells. Human herpes virus type 8 (HHV8) staining by immunohistochemistry (IHC) was positive, confirming the nail localisation of Kaposi sarcoma. Standard radiographs of the affected nails did not show any underlying bone lysis.

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Figure 1a:

Case 1: Nail dystrophy of the right big toe and 2^nd toe with purple-red discolouration.

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Figure 1b:

Onychoscopy of the big toe: Rainbow pattern (red circle), red-purplish areas of the nail bed (black arrow), scales (black circle), and peri-ungual erythema (red arrow) (dermoscope dermlite 4, 10x). Polarised light.

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Figure 1c:

Onychoscopy of the 2^nd toe showing red-purplish areas (black arrow) and scales (black circle) (dermoscope dermlite 4, 10x). Polarised light.

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Figure 1d:

Histological image showing dermal vascular proliferation with extravasation of red blood cells (Haematoxylin and eosin, 400x).

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Figure 1e:

Immunohistochemistry showing positive human herpes virus 8 (HHV8) staining (40x).

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Figure 2a:

Case 2: Erythematous-purplish plaque of the cuticle of the right big toe (black circle).

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Figure 2b:

Onychoscopy showing red-purplish cuticle. Polarised light (10x).

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Figure 3a:

Case 3 : Clinical examination showing purple-red discoloration, angiomatous papule of the proximal fold.

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Figure 3b:

Onychoscopy showing Rainbow pattern (red circle), red-purplish areas of the cuticle and proximal fold (black circle), scales (black arrow), peri-ungual erythema (red arrow) (dermoscope dermlite 4, 10x). Polarised light.

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Cases of nail damage in KS have been reported in rare instances. Frequent exposure to trauma could explain the appearance of lesions by Koebner phenomenon,¹ suggesting that it is probably underdiagnosed and underreported. Nail involvement can be associated with a cutaneous location,^1-3 as found in our patients, or can be indicative and exclusive of KS.^4-6

Clinically, nail involvement includes pincer nails, nail dystrophy, purple-red discoloration and sometimes even onycholysis. Purplish subungual/proximal nail fold nodule has been reported as a clinical presentation of exclusive nail forms.^5,6

Onychoscopy has an important role. It guides the diagnosis and detects subclinical damage. A few reports have described nail involvement in KS. Zinoune et al. described nail KS presenting as an erythronychial band, with onychoscopy revealing a large longitudinal red-purplish band starting from the matrix with degradation of its colour approaching the free edge of the nail.⁷ In our study, we found specific signs of KS: rainbow pattern, purple-red areas, red-purplish cuticle, and non-specific signs: nail dystrophy, peri-ungual erythema, sub-ungual hyperkeratosis, and onycholysis.

In the presence of associated skin involvement, the diagnosis of nail involvement is often easy especially if there are specific onychoscopic signs. However, isolated nail involvement can include differential diagnoses like pyogenic granuloma, exostosis, and melanoma without forgetting the tumours that can present in the form of longitudinal erythronychia, in particular, Bowen’s disease, onychopapilloma, and glomus tumour.⁶ However, the clinical and dermoscopic presentation only guides the diagnosis in certain situations, histology may be necessary to confirm it.

The definitive diagnosis is based on a nail biopsy, supplemented by immunohistochemistry. Histology reveals a proliferation of spindle cells with numerous intravascular and extravasated red blood cells, with positive HHV8 staining on IHC. This confirmation is necessary in the presence of isolated nail damage.⁶

In cases of nail KS, the dermatologist must systematically look for underlying bone lysis, by performing standard radiography, scintigraphy, or magnetic resonance imaging. This was confirmed in two patients as per the literature search.^1,5 A standard X-ray was done in all our patients, allowing bone involvement to be excluded.

To conclude, the presence of purple-red discolouration of cuticle, angiomatous papule or nodule, and an erythronychial band should suggest nail localisation of KS and should be confirmed on onychoscopy. Onychoscopy adds to and support the diagnosis of KS associated with confirmed cutaneous KS lesions even when histopathology of KS of nail lesions is not possible.