Background: The association between acne keloidalis nuchae (AKN) and thyroid diseases is yet to be investigated. Objective: To evaluate the risk of developing hypothyroidism and hyperthyroidism among patients with AKN and to characterize the patients who have AKN and thyroid comorbidities. Methods: A population-based cohort study was conducted comparing AKN patients (n = 2,677) with age-, gender-, and ethnicity-matched control subjects (n = 13,190) with regard to incident cases of hypothyroidism and hyperthyroidism. Adjusted hazard ratios (HRs) were estimated by Cox regression analysis. Results: The incidence rates of hypothyroidism among patients with AKN and controls were estimated at 2.15 (95% CI, 1.49-2.99) and 0.82 (95% CI, 0.66-1.00) cases/1000 person-years, respectively. The crude risk of developing incident hypothyroidism was 1.85-fold greater in patients with AKN (HR, 1.85; 95% CI, 1.24-2.78; P = 0.003). The elevated risk persisted following the adjustment for putative confounders (adjusted HR, 1.72; 95% CI, 1.03-2.89; P = 0.040). The risk of hyperthyroidism was comparable in patients with AKN and controls both in the crude (HR, 1.55; 95% CI, 0.57-4.22) and adjusted (adjusted HR, 1.92; 95% CI, 0.59-6.21) analyses. Patients with coexistent AKN and thyroid diseases were significantly older at the onset of AKN, had more prominent female preponderance, and had a higher burden of comorbidity. Conclusions: Patients with AKN are at an increased risk of hypothyroidism. Screening for hypothyroidism should be considered in AKN patients with a compatible clinical picture.
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