Clear Cell Acanthoma
Clear cell acanthoma (CCA), also called Degos acanthoma, is a rare benign epithelial tumor of epidermal keratinocytes. Rather than a true neoplasm, CCA is now regarded by most dermatopathologists as a reactive inflammatory hyperplasia driven by persistent local irritation or inflammation, in which the breakdown of intracellular glycogen comes to a complete halt.
Abnormal Glycogen Metabolism and Cytoplasmic Build-Up
- Reduced glycogen phosphorylase: The key cellular feature of CCA is reduced or absent activity of the enzyme glycogen phosphorylase in the affected epithelium. This stalls glycogen breakdown (glycogenolysis), so glycogen cannot be converted to glucose-1-phosphate.
- Cellular swelling: Glycogen packs the cytoplasm densely, pushing the nucleus to the edge and obscuring other organelles. When the tissue is fixed in standard formalin and stained with hematoxylin and eosin (H&E), the glycogen dissolves out, leaving pale, empty-looking clear cytoplasm.
Special Stains and Immunohistochemistry
- Periodic acid-Schiff (PAS) stain: The clear cytoplasm of CCA cells stains strongly PAS-positive (a vivid magenta) because of the polysaccharide bonds in glycogen.
- Diastase treatment (PAS-D): After the tissue is incubated with diastase, an enzyme that digests glycogen, the PAS positivity disappears completely (PAS-positive, diastase-sensitive). This is the gold-standard test for distinguishing CCA from malignant clear cell tumors (such as clear cell SCC or metastatic clear cell RCC, which contain diastase-resistant lipid or mucin).
Our Clinical Approach at Haute-Derma
Building on what we know about glycogen build-up in the cells and the proliferating capillaries in the papillary dermis, Haute-Derma follows a gentle, standardized protocol for clear cell acanthoma:
- Broad-spectrum dermoscopy: Detecting the characteristic string-of-pearls vessel pattern allows a quick diagnosis without the need for an extensive invasive biopsy.
- Dual-laser strategy: Vbeam Perfecta (595 nm) shuts down the proliferating capillary network, and an Er:YAG laser (2940 nm) then gently vaporizes the glycogen-laden clear cells point by point.
- Restoring the epidermal microenvironment: Regenerative boosters (exosomes / PDRN) help the wound heal quickly and reduce the risk of scarring.
Histopathology and Dermoscopic Criteria
Characteristic Histology Under the Microscope
Under the microscope, clear cell acanthoma is striking, because it stands out so sharply against the adjacent normal skin:
- Abrupt demarcation: The thickened epidermis (acanthosis) switches abruptly from normal keratinocytes to a band of swollen clear cells. The side borders are so sharp that you could draw a straight line between normal and abnormal tissue.
- Clear cytoplasm with an intact basement membrane zone (BMZ): The clear cells lie in layers just above the basal layer. The basement membrane is fully intact, with no breaks or invasion into the dermis.
- Neutrophilic microabscesses: Neutrophils leave the dilated papillary capillaries, pass through the epidermis and collect as tiny pockets of pus in the stratum corneum and upper spinous layer.
- Adnexal sparing: Sweat ducts (acrosyringium) and hair follicle openings that pass through the tumor are unaffected and keep their normal, darker-staining keratinocytes, creating "islands" of dark cells in a sea of clear cells.
Gold-Standard Dermoscopic Criteria
Digital dermoscopy at Haute-Derma picks up vascular signs that are pathognomonic for CCA:
- String-of-pearls pattern: Dotted (punctate) and glomerular vessels lined up one after another in parallel rows or gently curving arcs, like beads on a string.
- Wafer-like collarette of scale: The edge of the lesion is often rimmed by a thin, slightly peeling scale curling inward, reflecting the break in keratinization at the tumor's abrupt border.
- Homogeneous pink background: Caused by dilated papillary capillaries lying close to the surface under a thinned horny layer.
Clinical Features and Differential Diagnosis
Clinical Features
- Appearance: Usually a dome-shaped papule or raised plaque with a smooth, shiny or thinly scaly, slightly moist surface, ranging from bright red or orange-pink to red-brown.
- Size and fragility: Typically 0.5–2 cm across. It bleeds very easily with minor knocks (bleeding on minor trauma) because of the dense coils of papillary capillaries just beneath the surface.
- Typical location: More than 80% of cases are a single lesion on the lower limb (shin, thigh, calf) in middle-aged and older adults (40–70 years). Multiple lesions are rare.
Clinical and Histologic Comparison
| Clear Cell Acanthoma (CCA) | Clear Cell Squamous Cell Carcinoma (Clear Cell SCC) | Dermatofibroma |
|---|---|---|
| Benign, slow-growing | Malignant, invasive, fast-growing | Benign, collagen deposition |
| String-of-pearls vessels | Atypical vessels, central necrosis | Central white star-shaped area, peripheral pigment network |
| PAS (+) / diastase-sensitive (digested) | PAS (–/+) / diastase-resistant (not digested) | PAS (–) |
| Intact | Destroyed and invaded | Intact |
| Microabscesses concentrated in the horny layer | Mixed inflammatory infiltrate with necrosis | None or very few |
Precision Laser Treatment at Haute-Derma
Although clear cell acanthoma is benign, it rarely goes away on its own and is often a nuisance because it bleeds when it rubs against clothing. At Haute-Derma, our approach to CCA prioritizes gentle treatment, minimizing depressed scars and reducing the chance of recurrence:
Sealing the Feeding Vessels with Vbeam Perfecta 595 nm
Because CCA is packed with raised coiled capillaries in the papillary dermis, vaporizing it straight away would cause bleeding that obscures the doctor's view.
- Vbeam pulsed dye laser (595 nm): The laser energy is absorbed specifically by oxyhemoglobin in the vessel chains, coagulating the microvessels locally (selective photothermolysis).
- Goal: To cut off the tumor's blood supply, shrink it and create a "dry" field for the next vaporization step.
Vaporizing the Clear Cell Layer with Er:YAG 2940 nm / Superpulsed CO2 Laser
- Er:YAG 2940 nm (first choice): Because clear cells hold a lot of water-bound glycogen, the Er:YAG beam vaporizes them very precisely, removing only 5–10 µm per pass.
- Layer-by-layer ablation: The doctor precisely removes the glycogen-laden keratinocytes down to the level of the basement membrane. Because the vessels were sealed in step 1, the area bleeds little and the edges stay smooth.
Biological Repair and Scar Prevention
- Regenerative boosters: Stem cell-derived exosomes plus salmon DNA PDRN are micro-injected into the freshly treated base to encourage normal keratinocytes from the edges to migrate in and cover it.
- Moist wound healing: A hydrocolloid dressing keeps the wound in a physiologically moist environment so it heals within 3–5 days without a dry scab, keeping the risk of depressed or pitted scars on the leg to a minimum.
