Association of lichen planopilaris with hypothyroidism: a systematic review and meta‐analysis
Bibliographic record
Abstract
Lichen planopilaris (LPP) is a variant of lichen planus characterized by T-lymphocyte-mediated perifollicular inflammation leading to irreversible, scarring alopecia. It has an estimated prevalence between 0.03 and 0.04%.1, 2 Given the autoimmune pathophysiology of LPP, several recent studies have analyzed the association between LPP and autoimmune diseases, namely hypothyroidism. However, an association between LPP and hypothyroidism has been inconsistently reported in the literature, with studies both supporting3 and refuting4 such an association. Here, we analyze the association between LPP and hypothyroidism in meta-analysis. We performed a systematic review of the literature, adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and registered our protocol via PROSPERO (CRD42023422790). We searched EMBASE and MEDLINE from their dates of inception to April 2023 using the keywords “comorbidities,” “hypothyroidism,” “lichen planopilaris,” and “thyroid.” We included case–control studies that assessed the prevalence of LPP among cases and controls. Abstracts, case reports, case series, and cross-sectional studies without a control group were excluded. Study quality was assessed using the Newcastle–Ottawa scale. We calculated pooled odds ratio (OR) using a random effects model and evaluated study heterogeneity using the I2 statistic; publication bias was assessed using the Egger test. All analyses were performed using MedCalc software (version 20.305). Our initial search yielded 1,029 unique references; seven studies met our inclusion criteria, with a total of 1,664 LPP patients (Figure 1). Four studies reported positive, statistically significant associations between LPP and hypothyroidism, two studies demonstrated positive but statistically insignificant associations, and one study showed a negative, statistically insignificant association. Meta-analysis demonstrated an increased prevalence of hypothyroidism in LPP patients compared with controls (OR = 1.75, 95% CI: 1.46–2.21, P = 0.001, I2 = 57.4%). Egger test revealed nonsignificant publication bias (P = 0.76; Figure 2). Per the Newcastle–Ottawa scale, all studies (evaluated by two authors – TPJ and SK) were found to be of good quality. At present, the precise link between LPP and hypothyroidism remains to be elucidated, though several hypotheses may explain this association. As a T-lymphocyte-mediated process, LPP may share dysregulated T-cell/cytokine pathways with hypothyroidism. Such a hypothesis has been advanced to explain the association between alopecia areata and hypothyroidism.5 Additionally, there may be potentially overlapping human leukocyte antigen (HLA) restriction between LPP and hypothyroidism, causing aberrant licensing of T cells that attack both thyroid tissue and hair follicles. Limitations of our analysis include the inability to evaluate LPP severity or establish temporality between a diagnosis of hypothyroidism and LPP. Additionally, as only two of the seven studies presented disaggregated data by LPP subtype (i.e., LPP and frontal fibrosing alopecia), we were unable to perform subgroup analysis. We acknowledge that it would be valuable to study the association between hypothyroidism and LPP with stratification by LPP subtype. While LPP and frontal fibrosing alopecia are both T-cell-mediated diseases, potential differences in HLA variants associated with LPP or frontal fibrosing alopecia may impact the propensity of developing hypothyroidism. Nonetheless, our metanalysis is the first to report a link between LPP and hypothyroidism. Given this association, dermatologists may wish to elicit a thyroid review of systems when evaluating patients with LPP. Furthermore, patients with LPP may benefit from establishing care with a primary care physician and formal thyroid function studies, if indicated.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.006 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".