Hidradenitis suppurativa: the hair shaft carries the disease activity

Design

Integrated lipidomic analysis of human specimens with validation in a genetic mouse model

Population

Lesional hair, lesional skin and pus from patients with hidradenitis suppurativa; Ncstn conditional-knockout mice

Primary outcome

Lipid mediator profile and its relation to disease severity

Effect

Arachidonic acid and LTB4 dysregulated in all three specimen types; hair lipid signature correlated directly with severity

Hidradenitis suppurativa is judged clinically — Hurley stage, lesion counts, how much the patient can bear — and none of that is a biological measure of what the follicle is doing. This group took lipidomic profiles from three compartments in HS: lesional hair, lesional skin and pus. Arachidonic acid and leukotriene B4 were dysregulated across all three, and the lipid signature measured in lesional hair correlated directly with disease severity.

Mechanistically they describe a chain rather than a single culprit. Lipopolysaccharide from Gram-negative colonisers drives phosphorylation of cytosolic phospholipase A2-alpha in keratinocytes; recruited neutrophils amplify it through 5-lipoxygenase, producing LTB4 and extensive neutrophil extracellular traps. The same lipid pattern reproduced in Ncstn conditional-knockout mice, which are a genetic model of the disease.

Two things follow, neither of them a change in practice yet. First, a severity marker obtainable by pulling a hair rather than taking a biopsy would be genuinely useful in a disease where repeated sampling is painful and scarring — but correlation with severity in one cohort is a long way from a validated assay. Second, the Gram-negative and LTB4 arms are both already druggable, which makes this a target-identification paper with more than usual practical pull. Neither justifies changing antibiotic choice or adding a leukotriene antagonist today.

• Keep staging HS clinically; there is no validated lipid assay to order.
• Swab and culture genuinely purulent lesions rather than treating empirically on assumption.
• Address smoking and weight, which remain the modifiable factors with real evidence behind them.
• Do not start montelukast or similar for HS on the strength of a pathway paper.
• Record Hurley stage and lesion count at each visit so change is measurable without a biomarker.

Why it matters

It raises the possibility of measuring HS activity without cutting the patient.

Don't overread it

This is laboratory and animal work — no patient was treated on the basis of it.

The statistics, in plain English

The finding is a correlation between a lipid signature and disease severity within a single cohort, reported without a stated correlation coefficient or a validation set. That is the earliest stage a biomarker can be at: it shows the signal exists, not that it can classify a patient you have not already assessed. A biomarker becomes useful only when it is tested in a fresh cohort and shown to add something to what the clinician can already see.

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