Related Subjects:
|Nikolsky's sign
|Koebner phenomenon
|Erythema Multiforme
|Pyoderma gangrenosum
|Erythema Nodosum
|Dermatitis Herpetiformis
|Lichen Planus
|Acanthosis Nigricans
|Acne Rosacea
|Acne Vulgaris
|Alopecia
|Vitiligo
|Urticaria
|Basal Cell Carcinoma
|Malignant Melanoma
|Squamous Cell Carcinoma
|Mycosis Fungoides (Sezary Syndrome)
|Xeroderma pigmentosum
|Bullous Pemphigoid
|Pemphigus Vulgaris
|Seborrheic Dermatitis
|Pityriasis/Tinea versicolor infections
|Pityriasis rosea
|Scabies
|Dermatomyositis
|Toxic Epidermal Necrolysis
|Stevens-Johnson Syndrome
|Atopic Eczema/Atopic Dermatitis
|Psoriasis
Acanthosis Nigricans is a dermatological sign rather than a disease. Look for malignancy (gastric or liver) but most commonly associated with Type 2 diabetes It presents with dark, velvety hyperpigmentation of the skin and is most commonly associated with obesity and type 2 diabetes in the UK.
⚠️ In adults who are not obese, it may herald an underlying gastric or other internal malignancy.
ℹ️ About
- Acts as a cutaneous marker of insulin resistance.
- Can signal endocrine disorders, drug effects, or-rarely-cancer.
- Important to distinguish benign from malignant associations.
🩺 Clinical Features
- Velvety, hyperpigmented plaques that may look "dirty".
- Classically in the axillae, neck, and flexures; may also affect lips, palms, soles, and groin.
- More common in individuals with darker skin types.
- May be associated with pruritus or odour in some cases.
🧬 Aetiology
- Insulin Resistance: Most common cause (type 2 diabetes, obesity, metabolic syndrome).
- Hormonal Disorders: PCOS, Cushing’s, hypothyroidism, acromegaly.
- Medications: Oral contraceptives, corticosteroids, nicotinic acid, fusidic acid.
- Genetic/Familial: Rare, autosomal dominant, often presents in childhood.
- Malignancy: Especially gastric adenocarcinoma; also lung, breast, renal cancers.
Types
- Type I (Familial): Rare, AD inheritance, appears in childhood, not malignant.
- Type II (Benign Endocrine): Linked to acromegaly, Cushing’s, PCOS, hypothyroidism, diabetes.
- Type III (Insulin Resistance): Commonest; obesity/DM related, not malignant.
- Type IV (Drug-induced): Niacin, OCPs, glucocorticoids, testosterone. Seen in ~10% of renal transplant patients.
- Type V (Malignant): Adults, non-obese, sudden onset. Commonly gastric carcinoma, also lung and breast cancers.
🔎 Investigations
- Screen for insulin resistance: Fasting glucose, HbA1c.
- Baseline: FBC, ESR, U&E, LFT, TFTs.
- Malignancy screen if red flags (older age, non-obese, rapid onset): OGD, CT chest/abdomen/pelvis.
💊 Management
- 🎯 Treat the underlying cause: Weight loss, optimise diabetes control, treat endocrine disorders, stop causative drugs.
- 💊 Medical: Metformin for insulin resistance, topical retinoids/keratolytics for cosmetic benefit.
- 🔬 Oncology: Treat underlying malignancy where present.
- ✨ Cosmetic options: Laser therapy, dermabrasion in resistant cases.
Associations to Remember (Exam Tips)
- Type 2 diabetes & obesity (commonest cause).
- Gastric carcinoma (classic malignant association).
- PCOS in young women.
- Paraneoplastic syndrome in older non-obese adults.
References
