Acanthosis nigricans in the knuckles: An early, accessible, straightforward, and sensitive clinical tool to predict insulin resistance

Acanthosis Nigricans: An Updated Review

BACKGROUND

Early recognition of acanthosis nigricans is important because acanthosis nigricans can be a cutaneous manifestation of a variety of systemic disorders and, rarely, as a sign of internal malignancy.

OBJECTIVE

The purpose of this article is to familiarize pediatricians with the clinical manifestations, evaluation, diagnosis, and management of acanthosis nigricans.

METHODS

A search was conducted in November 2021in PubMed Clinical Queries using the key term "acanthosis nigricans". The search strategy included all clinical trials, observational studies, and reviews published within the past 10 years. Only papers published in the English literature were included in this review. The information retrieved from the above search was used in the compilation of the present article.

RESULTS

Acanthosis nigricans is characterized by symmetric, hyperpigmented, and velvety plaques with ill-defined borders, typically involving intertriginous areas. Obesity is the most common cause of acanthosis nigricans which is increasingly observed in obese children and adolescents and can serve as a cutaneous marker of insulin resistance. Early recognition of acanthosis nigricans is important because acanthosis nigricans can also be a cutaneous manifestation of a variety of systemic disorders and, rarely, as a sign of internal malignancy. This may consist of weight reduction, discontinuation of causative drugs, treatment of underlying endocrinopathy, or treatment of an underlying malignancy. For patients with isolated acanthosis nigricans and for those whose underlying cause is not amenable to treatment, treatment of the lesion may be considered for cosmetic reasons. Topical retinoids, vitamin D analogs, chemical peels, and other keratolytics are often used for the treatment of localized lesions. Seldom, systemic therapy such as oral retinoids may be considered for extensive or generalized acanthosis nigricans and acanthosis nigricans unresponsive to topical therapy. Other uncommon treatment modalities include dermabrasion, laser therapy, and surgical removal.

CONCLUSION

Although acanthosis nigricans is treatable, a complete cure is difficult to achieve. The underlying cause should be treated, if possible, to resolve and prevent the recurrence of acanthosis nigricans. The diagnosis is mainly clinical, based on the characteristic appearance (symmetrically distributed, hyperpigmented, velvety, papillomatous, hyperkeratotic plaques with ill-defined borders) and the typical sites (intertriginous areas, flexural area, and skin folds) of the lesions. The diagnosis might be difficult for lesions that have atypical morphology or are in an unusual location. Clinicians should be familiar with the clinical signs, evaluation, diagnosis, and therapy of acanthosis nigricans because of the link between it and underlying diseases.

Acanthosis nigricans in middle-age adults: A highly prevalent and specific clinical sign of insulin resistance

BACKGROUND

Insulin resistance (IR) precedes the diagnosis of many metabolic and non-metabolic illnesses, including type 2 diabetes mellitus (T2DM). Acanthosis nigricans (AN) is a clinical sign associated with IR. However, AN prevalence and diagnostic accuracy in middle-age adults before or at the time of prediabetes/diabetes diagnosis remain uncertain.

METHODS

With the aim to define AN prevalence and diagnostic accuracy, adults between 40 and 60 years of age were consecutively invited to participate in the study. Participants were categorised into one of two main groups: individuals with normoglycaemia (group 1) and hyperglycaemia (group 2 [ie, prediabetes/diabetes]). Demographic, clinical, anthropometric characteristics, homeostasis model assessment of IR, homeostatic model assessment of β-cell function, as well as the presence of AN on the neck, axillae, elbows and knuckles were assessed.

RESULTS

A total of 320 consecutive participants with a mean age of 49.3 years (59.4% women) were included. Overall, AN prevalence was 46.3%, while AN in group 1 and group 2 was 36.3% and 49.6%, respectively (P = .04). The most common affected sites in group 1 (n = 80) were the knuckles (21.2%) and the neck (17.5%), while in group 2 (n = 240), the neck (29.6%) followed by the knuckles (26.7%). The specificity and positive predictive value of AN for IR were 0.85 and 0.86 in group 1 and 0.90 and 0.96 in group 2, respectively.

CONCLUSIONS

In middle-age adults, within the entire spectrum of carbohydrate tolerance, AN is highly prevalent and specific. This finding supports its assessment as a reliable and convenient clinical sign of IR. The understanding of AN behaviour through different carbohydrate tolerance strata, and its different locations, could lead to early detection of individuals at high metabolic risk or help direct a more pathophysiological treatment approach in patients with T2DM.

Acanthosis Nigricans in the Knuckles of Infants: A Novel Clinical Marker of High Metabolic Risk

INTRODUCTION

Acanthosis nigricans (AN) is an early clinical sign of insulin resistance (IR) primarily in adults. The prevalence and association of AN and IR in infants, however, remains uncertain. We aimed to describe the prevalence of AN and its association with IR in a group of Latin-American infants.

METHODS

We studied a random sample of 227 healthy infants between 9 and 24 months of age. After a complete clinical history was obtained and a physical examination was performed, fasting plasma glucose and serum insulin were measured. Three blinded evaluators assessed AN in each patient. Infants with AN were categorized as cases. The HOMA-IR index cutoffs of ≥ 90th and ≥ 95th percentiles were considered IR.

RESULTS

There were 49 infants with AN (21.6%) (cases) and 178 without AN (78.4%) (controls). Cases had a significantly higher mean serum insulin, fasting plasma glucose, and HOMA-IR levels of 3.67 ± 2.56 µU/ml vs. 2.42 ± 1.45 µU/ml, P = 0.005; 84.2 ± 12.6 mg/dL vs. 77 ± SD 9.9 mg/dL, P ≤ 0.001; HOMA-IR 0.77 ± 0.54 vs. 0.46 ± 0.28, P ≤ 0.001, respectively. More cases than controls presented HOMA-IR levels ≥ 95th percentile (cases 18.4%; controls 0.5%, P ≤ 0.001) and ≥ 90th percentile (cases 32.7%; controls 1.6%, P ≤ 0.001). AN in the knuckles had a high sensitivity and a negative predictive value (NPV) for detecting patients with HOMA-IR levels above the 95th percentile (sensitivity 90%; NPV 99.4%) and above the 90th percentile (sensitivity 84.2%; NPV 98.3%).

CONCLUSION

AN in the knuckles is a prevalent, non-invasive, costless, and reliable screening clinical tool that can be used for early detection of infants with IR and a high metabolic risk.