Sandpaper Rash on Sun-Exposed Skin: Diagnosis and Treatment
The most likely diagnosis is actinic keratoses (AKs), which should be treated based on lesion number and characteristics—cryosurgery or topical 5-fluorouracil for multiple thin lesions, with curettage reserved for hypertrophic lesions requiring histological confirmation. 1
Differential Diagnosis
The sandpaper-like texture on sun-exposed skin most commonly represents:
- Actinic keratoses: Discrete or confluent patches of erythema and scaling on chronically sun-exposed skin (face, dorsal hands, scalp) in fair-skinned middle-aged to elderly individuals 1
- Pellagra: If accompanied by diarrhea and dementia, consider niacin deficiency presenting as bilaterally symmetrical erythema resembling sunburn on sun-exposed areas 2, 3
Key distinguishing features to assess:
- Distribution pattern: AKs favor face, scalp, ears, dorsal hands 1
- Associated symptoms: Pellagra presents with the "3 D syndrome"—dermatitis, diarrhea, dementia 2, 4
- Dietary history: Poor nutrition, chronic alcoholism, or malabsorption suggests pellagra 3, 5
- Texture: AKs are keratotic with rough, sandpaper-like feel 1
Treatment Algorithm for Actinic Keratoses
For Low Number of Lesions (Few Discrete AKs)
- Cryosurgery: First-line for isolated lesions on scalp, ears, nose, cheeks, forehead 1
- 5-Fluorouracil (5-FU): Equally effective for low numbers, allows self-treatment 1
- Curettage: Reserved for hypertrophic lesions or those failing other therapies, with histological confirmation 1
For High Number of Lesions (Multiple or Confluent AKs)
- 5-Fluorouracil: Most effective for extensive involvement 1
- Imiquimod: Alternative for multiple lesions, particularly useful for self-reliant patients 1
- Diclofenac gel: Option for high numbers with lower efficacy 1
Site-Specific Considerations
- Scalp (confluent): Pretreatment with 5% salicylic acid ointment improves outcomes with 5-FU or imiquimod 1
- Dorsal hands: Extended treatment courses needed; consider pretreatment with salicylic acid 1
- Periorbital area: Cryosurgery or curettage preferred as topical therapies difficult to apply 1
- Below knee: Photodynamic therapy (PDT) preferred due to poor healing risk with other modalities 1
For Hypertrophic or Treatment-Resistant Lesions
- Curettage with histology: Essential to exclude invasive squamous cell carcinoma 1
- Formal excision: May be required if malignancy suspected 1
Treatment for Pellagra (If Diagnosed)
If the triad of dermatitis, diarrhea, and dementia is present with poor nutritional history, immediately initiate nicotinamide supplementation with dramatic improvement expected within 3 days. 3, 5
- Nicotinamide or niacin: Exogenous administration cures pellagra 2, 4
- B-complex vitamins: Include other B vitamins, zinc, and magnesium 2, 4
- High-quality protein diet: Essential for tryptophan precursor 2, 3
- Topical emollients: Reduce skin discomfort 2
Critical Pitfalls to Avoid
- Do not dismiss as simple "sun damage": AKs carry risk of progression to invasive squamous cell carcinoma, though individual risk is low 1
- Do not overlook pellagra: This deadly but curable condition still occurs in vulnerable populations with poor nutrition, chronic alcoholism, or malabsorption 3, 5, 6
- Do not use cryosurgery below the knee: Risk of poor healing and ulceration; PDT preferred 1
- Do not ignore treatment failures: Hypertrophic or resistant lesions require histological assessment to exclude malignancy 1
- Do not confuse with EGFR-inhibitor rash: Drug-induced acneiform eruptions occur in cancer patients but lack the keratotic sandpaper texture and show follicular papules/pustules 1