Worldwide, more than 1.9 billion adults are overweight, and around 600 million people suffer from obesity. Similarly, ~382 million individuals live with diabetes, and 40–50% of the global population is labeled at “high risk” (i.e., prediabetes). The impact of these two chronic conditions relies not only on the burden of illnesses per se (i.e., associated increased morbidity and mortality), but also on their increased cost, burden of treatment, and decreased health-related quality of life. For this review a comprehensive search in several databases including PubMed (MEDLINE), Ovid EMBASE, Web of Science, and Scopus was conducted. In both diabetes and obesity, genetic, epigenetic, and environmental factors overlap and are inclusive rather than exclusive. De facto, 70–80% of the patients with obesity and virtually every patient with type 2 diabetes have insulin resistance. Insulin resistance is a well-known pathophysiologic factor in the development of type 2 diabetes, characteristically appearing years before its diagnosis. The gold standard for insulin resistance diagnosis (the euglycemic insulin clamp) is a complex, invasive, costly, and hence unfeasible test to implement in clinical practice. Likewise, laboratory measures and derived indexes [e.g., homeostasis model assessment of insulin resistance (HOMA-IR-)] are indirect, imprecise, and not highly accurate and reproducible tests. However, skin manifestations of insulin resistance (e.g., acrochordons, acanthosis nigricans, androgenetic alopecia, acne, hirsutism) offer a reliable, straightforward, and real-time way to detect insulin resistance. The objective of this review is to aid clinicians in recognizing skin manifestations of insulin resistance. Diagnosing these skin manifestations accurately may cascade positively in the patient’s health by triggering an adequate metabolic evaluation, a timely treatment or referral with the ultimate objective of decreasing diabetes and obesity burden, and improving the health and the quality of care for these patients.

AN occurs with a high prevalence in Latin American youths, and its prevalence is much higher in a "non-classical" and ignored location where it is very easy to detect during physical examination: the knuckles. It may also occur earlier in this location in the evolution to obesity. The presence of AN in the knuckles in any patient, even if they have a normal body mass index, might indicate the likelihood of an early clinical manifestation of insulin resistance and metabolic consequences.

Background Castleman disease (CD) is a lymphoproliferative B-cell disease that is diagnosed from lymphoid hyperplasia with vascular proliferation. Symptoms may include fever, night sweats, and weight loss. Cutaneous manifestations often may go unnoticed since little has been described in the literature regarding them. Materials and Methods A search of CD with cutaneous manifestations was performed in PUBMED, ProQuest, Ovid, Scopus, EMBASE, and Medline. All articles included patients over 18 years of age with a diagnosis of CD and cutaneous manifestations. Results A total of 68 articles were included. The most common cutaneous manifestations include paraneoplastic pemphigus and erythematous-brown plaques, papules, or nodules. Patients presenting with these manifestations should always have a thorough physical exam, and clinicians should try to identify any palpable lymph nodes. A complete workup to rule out other neoplasias needs to be performed as well. Conclusions A better understanding of these skin manifestations of CD may help physicians promptly diagnose and reconsider the path of diagnostic tests to identify this entity.

Any clinical/biochemical marker revealing obesity or diabetes before their appearance is valuable. Insulin resistance (IR) is present in both disorders many years before occurrence. Accordingly, we determined whether acanthosis nigricans (AN) in the knuckles is associated to higher insulin and homeostasis model assessment for estimated insulin resistance (HOMA-IR) index values, and assessed the influence of body-mass index (BMI) and the diagnostic performance of AN in the knuckles to detect IR. In this cross-sectional controlled study, we included men or women, 18 to 23 years old, with or without AN in the knuckles. In 149 cases with AN in the knuckles and 145 controls, fasting insulin was higher in cases (13.45 µU/mL ± 7.8 vs. 8.59 µU/mL ± 3.63, P < .001, respectively). Mean HOMA-IR index was also higher (2.86 ± 1.68 vs. 1.78 ± 0.77, P < .001). A significant increase in fasting insulin and HOMA-IR values between and within BMI groups from normal through obese category was identified in controls and cases. By multivariate regression analysis, cases with normal BMI were significantly associated to a HOMA-IR ≥2.5 (OR = 3.09, CI95% = 1.75–5.48, P = .001). A model of AN in the knuckles, normal BMI, and increased waist circumference allowed identifying 2 out of 3 cases with HOMA-IR index ≥2.5. AN in the knuckles could be addressed with two aims: as an easy, accessible, and costless diagnostic tool suggesting hyperinsulinemia secondary to IR, and, an early marker of IR even in the absence of overweight or obesity.