Acanthosis

by S. Serkan Sezer MD

Acanthosis is a dermatological term that describes a specific pattern of change in a particular layer of the skin. Although the word may sound unfamiliar, conditions that fall under this heading are encountered relatively often in everyday clinical practice. The term may refer simply to a microscopic finding, or it may form part of the name of a distinct disease — most notably acanthosis nigricans.

Definition

In English medical dictionaries, the term is transcribed as /ˌækænˈθəʊsɪs/ and defined as “a disease of the prickle cell layer of the skin, where warts appear on the skin or inside the mouth.”

In modern usage the word carries two related meanings:

  1. As a microscopic (histological) finding — thickening of the stratum spinosum, or “prickle cell layer,” of the epidermis. The prickle cells are the layer of keratinocytes connected to one another by tiny spine-like attachments (desmosomes); when their number increases, the epidermis becomes thicker. Pathologists describe this finding simply as acanthosis.
  2. As part of a disease name — most notably acanthosis nigricans, a clinical condition characterised by dark, thickened, velvety patches of skin, often associated with systemic disorders.

The word derives from the Greek akantha, meaning “thorn” or “spine” — a reference to the spine-like appearance of the prickle cells.

The Prickle Cell Layer

To understand acanthosis, it helps to know a little about the structure of the epidermis. The epidermis is built up of several layers; from deep to superficial these are:

  • Stratum basale — the basal cell layer, where new cells are produced.
  • Stratum spinosum — the prickle cell layer, with characteristic spine-like cell-to-cell connections.
  • Stratum granulosum — the granular layer.
  • Stratum lucidum — a thin clear layer, present mainly in thick skin such as the palms and soles.
  • Stratum corneum — the outermost, keratinised horny layer.

When the prickle cell layer thickens beyond normal — that is, when there is acanthosis — the skin in that area appears clinically thicker, often darker, and sometimes verrucous or wart-like.

Acanthosis Nigricans

The condition most commonly referred to in everyday clinical practice when the word “acanthosis” is used is acanthosis nigricans. Its characteristic features are:

  • Skin colour change — brown-black, dark, “dirty-looking” patches.
  • Thickening of the skin — a soft, velvety surface.
  • Wart-like (verrucous) appearance — small skin-tag-like lesions may develop on the surface.
  • Typical sites — the back of the neck, armpits (axillae), groin, knuckles, and skin folds beneath the breasts.

The condition itself is usually painless and does not cause itching; the main complaint is often cosmetic. Its real importance lies in the fact that it can be a clue to an underlying systemic problem.

Causes

Acanthosis nigricans can develop in a number of different settings:

1. Insulin Resistance and Diabetes

The most common cause. High levels of insulin in the blood stimulate skin cells, leading to thickening and darkening. It is therefore frequently seen in:

  • Type 2 diabetes
  • Obesity
  • Metabolic syndrome
  • Polycystic ovary syndrome (PCOS)

2. Hormonal Disorders

  • Cushing’s syndrome
  • Acromegaly
  • Hypothyroidism
  • Addison’s disease

3. Medications

Some drugs can trigger the condition:

  • High-dose niacin (nicotinic acid)
  • Corticosteroids
  • Oral contraceptives
  • Some growth hormone preparations

4. Genetic Forms

Inherited variants, sometimes apparent from childhood, in which the condition is passed on within families.

5. Malignant Acanthosis Nigricans

A particularly important form. It tends to appear suddenly, progress rapidly, and involve unusual sites such as the mouth, lips, and palms. It is most commonly associated with cancers of the gastrointestinal tract — especially gastric (stomach) adenocarcinoma. Its appearance can in some cases precede the diagnosis of the underlying cancer, which is why it must never be ignored.

Diagnosis

The diagnosis is usually straightforward on clinical examination. However, identifying the underlying cause requires further investigation:

  • Detailed history — onset, rate of progression, family history, medications.
  • Physical examination — distribution and characteristics of the lesions, body mass index, signs of insulin resistance.
  • Blood tests — fasting blood glucose, HbA1c, insulin levels, lipid profile, thyroid function tests, hormone levels.
  • Skin biopsy — sometimes used when the diagnosis is uncertain or to exclude other conditions.
  • Cancer screening — particularly when malignant acanthosis nigricans is suspected, investigation of the upper gastrointestinal tract and other organs may be needed.

Treatment

Treatment is directed primarily at the underlying cause:

Treating the Underlying Condition

  • Weight loss — in obesity-related cases, weight reduction is the single most effective measure.
  • Management of diabetes — improvement in blood glucose control often improves the skin appearance.
  • Hormone treatment — correcting underlying hormonal disorders.
  • Discontinuing offending drugs — when a medication is responsible, withdrawing it (under medical supervision) is appropriate.
  • Cancer treatment — in the malignant form, treating the underlying tumour is the priority.

Topical Treatments

A range of topical agents may be used for cosmetic improvement:

  • Topical retinoids (tretinoin, adapalene)
  • Salicylic acid
  • Urea-containing creams
  • Topical vitamin D analogues
  • Ammonium lactate

Other Approaches

  • Chemical peels
  • Laser therapy
  • Dermabrasion

It is important to remember that these methods provide cosmetic improvement only. If the underlying cause is not addressed, the condition tends to return.

Other Forms of Acanthosis

The term is also used in some other contexts:

  • Acanthosis palmaris (tripe palms) — thickening of the palms with a corrugated, “tripe-like” appearance, often associated with internal malignancy.
  • Oral acanthosis — thickening of the lining of the mouth, which may be seen in some systemic conditions.

When to See a Doctor

Medical assessment is advisable in the following situations:

  • Newly developing dark, thickened patches of skin
  • Lesions appearing on the neck, armpits, or skin folds
  • A sudden change in skin appearance, particularly in adulthood
  • Skin changes accompanying weight gain
  • A family history of diabetes or metabolic disorders
  • Unintentional weight loss together with skin changes (warrants prompt evaluation)

Importance and Significance

Acanthosis nigricans is much more than a cosmetic problem. It can be an early sign — a “skin signal” — of important underlying conditions such as insulin resistance, diabetes, hormonal disorders, or, in rarer cases, malignancy. For this reason, dermatologists often refer to it as a “warning sign on the skin.” Detection should prompt a careful search for the underlying cause.

Disclaimer

The information provided here is intended for general informational and educational purposes only and does not constitute medical advice, diagnosis, or treatment. If you notice changes in the colour, thickness, or texture of your skin, please consult a qualified dermatologist or other healthcare professional. The investigation and management of acanthosis nigricans and other forms of acanthosis should be carried out under medical supervision. Do not rely on the content of this article when making decisions about your own or another person’s medical care.