1. Clear cell acanthoma or Degos' acanthoma

2. Clear cell acanthoma 
Clear-cell acanthoma (CCA), first described by Degos et al. in 1962, is a rare benign skin lesion which occurs mostly on the lower limbs of middle-aged to elderly individuals, peaking in incidence in the fifth decade of life. It is usually a solitary red to brown papule, glistening nodule, or dome-shaped plaque measuring 2-20 mm, with a crusted or scaly surface, sometimes oozing a clear fluid or, occasionally, blood. CCA has been clinically described as presenting the 'stuck on' appearance of seborrheic keratosis (SK), the vascular look of a pyogenic granuloma, the scaling and exsudation of an eczema, and the advancing round border of an epithelioma. Despite these characteristics, CCA is rarely clinically diagnosed prior to biopsy, since basal cell carcinoma (BCC), SK, and squamous cell carcinoma (SCC), among other conditions, are most often suspected.  Regarding these features and the fact that most patients present with a single lesion, CCA was formerly considered neoplastic in nature. However, given its close histopathological resemblance to psoriasis and occasional associations and/or lesion overlapping with several conditions, including psoriasis itself, a reactive/inflammatory process has been favored by many researchers. CCA may occur either as a single or as multiple lesions.  Rare disseminated forms must be differentiated from other eruptive dermatoses such as guttate psoriasis, certain forms of parapsoriasis, sarcoidosis, lichen planus, and granuloma annulare. 

3. Clear cell acanthoma 
The histopathological picture of CCA is quite typical, consisting of epidermal hyperplasia, a slight increase in size of the Malpighian cells - which have a pale cytoplasm -, spongiosis, and parakeratosis. The PAS-positive and diastase-labile pale-cell acanthosis shows a distinct line of demarcation and does not involve either acrosyringia or acrotrichia.  Shared histopathological features with psoriasis include parakeratosis, hypo-/agranulosis, regularly elongated rete ridges, intracorneal/intramalpighian neutrophil aggregates, papillary-dermal edema, and dilated/tortuous capillaries. Immunoreactivity for epithelial membrane antigen (EMA) by clear cells can also assist in defining the diagnosis.  A broad spectrum of tumors composed of large clear cells should be considered in the histopathological differential diagnosis of CCA, including clear-cell hidradenoma, clear-cell syringoma, hidroacanthoma simplex, tricholemmoma, and SCC in situ. In psoriasiform keratosis, in which psoriasiform hyperplasia and intraepithelial neutrophils are seen, may also be considered for the differential diagnosis of CCA The clinical differential diagnosis is broad and includes basal cell carcinoma, squamous cell carcinoma, Bowen's disease, actinic keratosis, hemangioma, dermatofibroma, inflamed seborrheic keratosis, verruca vulgaris, amelanotic melanoma, psoriasis, histiocytoma, eczematous dermatitis, nevus, parapsoriasis , pyogenic granuloma,Kaposi sarcoma and B-cell lymphoma

4. Clear cell acanthoma
A – A bright-red, lobulated plaque with an oozing-surface on the left nipple and areola (original presentation in 2004); B – Bright erythematous, eczematoid plaque with a slightly mamillated surface and ill-defined hyperchromatic margins (year 2010); C – Psoriasiform hyperplasia with diffuse clear-cell change of keratinocytes in the Malpighian layer and fusion of rete ridges (H-E, original magnification 100x); D – Clear cells stained in red, basal cell layer spared (PAS, original magnification 100x); E –Clear cells failed to stain with PAS after diastase digestion (PAS-diastase, original magnification 100x); F – Intense expression of EMA by clear cells (EMA immunoperoxidase, original magnification 100x) 

5. Clear cell acanthoma 
A – Somewhat raised, infiltrated plaque on the left nipple/areola with eroded, wet surface and well-defined margins; B – Elongated, fusioned, club shaped rete ridges with numerous clear cells. Note papillary-dermal edema, elongated capillaries, and inflammatory cell infiltrate (H-E, original magnification 100x); C – Eroded epidermis, congestive capillaries, and erythrocyte extravasation beside an acantotic epidermis with intense clear-cell change; D – Neutrophils scattered among clear cells (H-E, original magnification 400x); E – Mixed interstitial and perivascular inflammatory cell infiltrate composed of lymphocytes and numerous eosinophils (H-E, original magnification 400x); F – Intense expression of EMA by clear cells (EMA immunoperoxidase, original magnification 100x) 

6. Clear cell acanthoma Clinical features of the lesion include:
Clear cell acanthoma is a rare benign (non-cancerous) epithelial skin tumour. It is usually a solitary lesion appearing on the lower legs but there have been cases of multiple lesions occurring.
Clear cell acanthoma are also known as Degos acanthoma or acanthome à cellules claires.
Clinical features of the lesion include:
@ Slightly elevated to dome-shaped plaque or nodule
@ Color varies from pink to brown, but is most commonly blood red and shiny
@ Can be from 3 to 20mm in diameter
@ Wafer-like crusty scale may be stuck round the edges of the lesion. A moist or bleeding surface may result if scale is removed.
How do you get clear cell acanthoma and who is at risk?
It is currently not known why clear cell acanthoma occur. Although rare, they occur mostly in adults of middle-age or older. Both male and females can be affected.
Diagnosis :
The diagnosis is rarely made before skin biopsy. However, dermatoscopy is characteristic, as the blood vessels are lined up in strings (see images above). When examined under the microscope, clear cell acanthoma show a characteristic accumulation of clear glycogen-containing cells in the epidermis.
Treatments :
They may persist for years and years without changing or causing any complications. They are easily excized.

7. Clear cell acanthoma: clinical view

8. Clear cell acanthoma: dermoscopic views

9. Multiple eruptive clear cell acznthoma J Dermatol Case Rep
The epidermal cells showed clear cytoplasm and abundant glycogen, as demonstrated by positive period acid-Schiff (PAS) staining and removal of the staining after diastase digestion

10. Multiple giant clear cell acanthomas IJDVL: 2016 : 82 : 2 : 218
Appearance of the posterior side of lower extremities (a). There was a 40 mm × 30 mm red, sharply demarcated nodule and 10 mm × 20 mm satellite papulonodules around it on her posterior side of right leg (c). There was scattered 5 mm, 10 mm, 15 mm papules and nodules with sharply demarcated margins and a thin collateral rim of scale on her posterior side of both lower extremities (b,d and e)

11. Multiple giant clear cell acanthomas IJDVL: 2016 : 82 : 2 : 218
On histological examination epidermal acanthosis, pale appearance of the keratinocytes and intraepidermal neutrophils were seen. In the dermis, there was proliferation of blood vessels and perivascular infiltration of lymphocytes, histiocytes and neutrophils. (a) H and E, ×40 (b) H and E, ×100 (c) H and E, ×100 (d) H and E, ×200

12. Clear cell acanthoma of Degos
Vascular punctae present (black arrows)
Dermoscopic appearance of same lesion showing the ''string of pearls''

13. Giant clear cell acanthoma with keratoacanthoma-like changes:
The tumor is composed of an exophytic component as well a central endophytic component with cystic change.Figure 3. At its periphery, the tumor displayed typical features of clear cell acanthoma, namely, psoriasiform epidermal hyperplasia with pale keratinocytes. The pale area is clearly demarcated from adjacent epidermis with numerous infiltrating neutrophils.
Giant clear cell acanthoma with keratoacanthoma-like changes:
D Online Journal 12 (4): 11

14. Histology of clear cell acanthoma

16. Clear cell acanthoma histology

17. Clear Cell Acanthoma
Large cell acanthoma usually presents as a well demarcated solitary plaque or scaly, lightly pigmented patch on sun exposed skin. HPV type 6 is considered an important cofactor in the pathogenesis of  large-cell acanthomas.
Site:  Usually located on the face, or on the limbs and trunk.
Microscopic features:    
Histopathological examination reveals sharp demarcation of the lesion from the normal epidermis.
The thickened epidermis consists of enlarged keratinocytes, twice the  normal size.
Other features include basket weave orthokeratosis, prominent hypergranulosis and hyperpigmentation of basal layer.
In the dermis telangiectasia, solar elastosis  and chronic inflammation may be present.
Differential diagnosis includes solar lentigo and solar keratosis. 
(In solar keratosis there is parakeratosis, in large cell acanthoma there is orthokeratosis)

18. Clear Cell Acanthoma

19. Giant clear cell acanthoma with keratoacanthoma-like
Cytoplasm of the pale cells is positive with periodic-acid-Schiff (PAS) stainFigure 5. The staining is removed by diastase digestion (PAS-D)
Giant clear cell acanthoma with keratoacanthoma-like
D Online Journal 12 (4): 11 :

20. clear cell acanthoma Histologic Features A well demarkated lesion with
Confluent parakeratosis containing neutrophils and plasma
Marked psoriasiform hyperplasia with thick fused rete ridges
Keratinocytes with abundant clear cytoplasm
Neutrophils and nuclear dust in the epidermis
Hypogranulosis and very thin suprapapillary plates
Scattered dyskeratotic cells
Marked edema and hypervascularity of the papillary dermis
A moderately dense lymphohistiocytic perivascular infiltrate with many plasma cells

21. Clear cell acanthoma histology

23. Vascular patterns in dermoscopy

24. Vascular patterns in dermoscopy