Welcome back to the journal review. This is the March 2026 issue of Dermatologic Surgery, and we've got four pieces worth your time this month — a randomized trial on laser treatment for lichen simplex chronicus, a retrospective look at what happens when shave biopsies transect melanoma, a short but practical infection-rate study on Mohs surgery with lip wedge repair, and an advisory statement that's going to make you rethink your penicillin-allergy antibiotic algorithm. Let's get into it.

First up is an original article, a randomized controlled trial out of Cairo University looking at fractional carbon dioxide laser for lichen simplex chronicus. The clinical problem here is familiar to all of us — lichen simplex chronicus is that thick, lichenified, relentlessly itchy plaque driven by the itch-scratch cycle, affecting something like one in eight people in the general population, skewed toward middle-aged women. Topical corticosteroids are first-line, but they don't always break the cycle, and the authors note that controlled data on fractional carbon dioxide laser — which has shown antipruritic benefit in things like hypertrophic scars, prurigo nodularis, and cutaneous amyloidosis — is basically absent for this specific indication. So the gap is real: does adding or substituting laser for steroid actually help, in a controlled fashion, rather than just anecdotally?

Methodologically, this was a prospective three-arm randomized trial, sixty patients with biopsy-confirmed lichen simplex chronicus, randomized by closed envelope into topical betamethasone valerate alone, fractional carbon dioxide laser alone, or the combination, all for three months. One thing worth flagging for your own methodological radar: the steroid arm had thirty patients while the laser and combination arms had fifteen each — the paper doesn't explain that allocation, but my read is that they likely wanted a more robust reference dataset on the active control arm since that's the existing standard of care, while treating the laser arms as more exploratory. That's my inference, not the authors' stated rationale. Assessment was appropriately split into patient-reported outcomes — a twelve-item pruritus severity scale and a visual analog scale for itch — and blinded physician-reported outcomes covering erythema, lichenification, scaling, excoriation, and an Investigator's Global Assessment. Having a blinded assessor for the physician-reported outcomes is the right call here, since obviously nobody could blind the patient or treating physician to whether they were getting a laser session.

On results: all three groups improved significantly from baseline, which isn't surprising. The primary outcomes were the head-to-head comparisons. For achieving an Investigator's Global Assessment of clear or almost clear, the combination arm hit that mark in about nine in ten patients, the laser-alone arm in about two-thirds, and the steroid-alone arm in about half — and that difference across groups was statistically significant. For achieving at least a fifty percent improvement on the itch visual analog scale, it was essentially universal in the combination group, versus roughly seven in eight in the laser group and two-thirds in the steroid group — again statistically significant. Several secondary comparisons — percentage reduction in itch severity scores, in the visual analog scale, in erythema and lichenification — trended in the same direction, combination and laser outperforming steroid alone, but did not reach statistical significance, so those should be read as suggestive rather than proven.

On limitations, the authors don't spell out an exhaustive list, but a few things jump out on your own critical read: the unequal group sizes reduce power in the laser-only and combination arms specifically; there was a baseline imbalance in erythema severity across groups that reached statistical significance, which muddies the physician-reported erythema comparisons somewhat; and there's no long-term follow-up here to tell you about durability of response or recurrence after stopping treatment, which matters enormously for a chronically relapsing itch-scratch condition.

Practically, here's where I'd land: this is an interesting, well-designed pilot-sized trial suggesting fractional carbon dioxide laser has real antipruritic and lichenification-reducing effect in this disease, and that combining it with topical steroid outperforms steroid alone. It is not yet practice-changing in the sense of displacing topical steroids as first-line — but if you have a patient with recalcitrant, thick, monomorphic lichen simplex chronicus plaques on the hands, feet, or lower extremities who's failed or plateaued on topical steroid, this gives you a reasonable, mechanistically plausible evidence-based option to add fractional ablative laser to the regimen, particularly if you already have that device in your practice.

Second article, and this one is squarely in Mohs and dermatologic oncology territory — a single-institution retrospective cohort study asking what actually happens, outcome-wise, when melanomas are transected at the deep margin on shave biopsy. You all know the concern: tangential shave biopsy is fast, convenient, and cosmetically favorable if the lesion turns out benign, but it carries a real risk of cutting through the base of an invasive melanoma, which threatens your ability to accurately assign Breslow depth — and Breslow depth drives staging, sentinel node decision-making, and adjuvant therapy eligibility. The gap here is whether that transection actually translates into worse patient outcomes, or whether it's more of a staging-accuracy problem that gets absorbed into management decisions without truly changing prognosis.

The design was a retrospective chart review at Marshfield Clinic, patients diagnosed with melanoma over an eleven-year span, restricted to those biopsied by shave technique, with outcomes compared between transected and nontransected tumors and then re-analyzed after stratifying by American Joint Committee on Cancer eighth-edition T stage. Retrospective design here is really the only option — you can't ethically or practically randomize biopsy technique on suspicious melanocytic lesions — and the T-stage stratification is the crucial methodological move, since transection status and tumor depth are obviously entangled: deeper, more advanced tumors are inherently harder to fully sample with a razor blade, so any raw comparison between transected and nontransected tumors is going to be badly confounded by depth unless you control for it.

And that's exactly what the results show. Of a hundred and twelve shave-biopsied melanomas, roughly three in ten were transected at the deep margin, a significantly higher transection rate than either punch or excisional biopsy showed in this same population. In the unadjusted analysis, transected tumors had dramatically worse everything — five-year recurrence around one in four versus about one in thirteen, five-year mortality around one in three versus one in ten, and melanoma-specific mortality roughly one in five versus one in forty, all statistically significant. But — and this is the key finding — once you stratified by T stage, none of those differences in recurrence, metastasis, or mortality remained significant. In other words, the worse outcomes tracked with the fact that transected tumors were, on average, simply deeper and higher-stage to begin with, not with transection itself. The one outcome that did remain significant after stratification was sentinel lymph node biopsy rate in the shallowest tumors — transected T1 melanomas underwent sentinel node biopsy about six in ten times, compared with roughly one in four for nontransected T1 tumors, without a corresponding increase in actual node positivity.

The authors' discussion is appropriately measured: they interpret this as evidence that transection itself doesn't appear to independently drive worse biology or survival once you account for depth, but it does drive over-staging and, consequently, unnecessary sentinel node biopsies in thin melanomas — procedures that carry real cost and morbidity without oncologic benefit if the true depth would have kept the patient below the sentinel node threshold. They looked for an easy explanation, like transected thin tumors simply being wider and thus harder to shave at an adequate angle, but lesion diameter didn't significantly differ between transected and nontransected thin tumors, so they conclude this is more a technique issue than a lesion-size issue. Limitations are clearly stated by the authors themselves — small sample size limiting power, single-institution and rural population limiting generalizability, no data on the clinician's pre-biopsy suspicion for melanoma which likely influences technique choice, exclusion of patients with inadequate follow-up introducing possible selection bias, and a fifteen-year study window during which melanoma staging criteria and treatment guidelines themselves evolved.

The practical takeaway for you: this doesn't change how you manage a melanoma once diagnosed, and it's reassuring in the sense that transection doesn't appear to independently worsen prognosis when true depth is accounted for. But it's a strong technique reminder, especially relevant if you or your referring clinicians are doing the initial biopsies — saucerize deep enough to capture full Breslow depth, particularly on lesions that look like they could be thin melanomas, because getting that depth wrong doesn't just create an academic staging problem, it can trigger a sentinel lymph node biopsy that the patient never actually needed.

Third, a short communications piece — really a focused retrospective case series — on postoperative infection after Mohs surgery with full-thickness lip wedge repair. The setup: the 2008 advisory statement on prophylactic antibiotics in dermatologic surgery recommends prophylaxis for lip wedge excision, citing an infection rate of about eight and a half percent — but that number comes from a single prospective study of only thirty-five combined ear and lip wedge cases, and nobody has specifically looked at Mohs surgery with full-thickness lip wedge repair, which the authors argue is a fundamentally similar procedure. So this is a straightforward attempt to generate procedure-specific infection data.

This was a two-surgeon, single-institution retrospective review at the University of Rochester spanning 2017 to 2024, capturing two hundred fifty-nine cases of Mohs surgery with full-thickness wedge repair of the lip involving mucosa and muscularis. Notably, none of these patients received prophylactic antibiotics at any point — before, during, or after surgery — which makes this essentially a natural experiment on infection rate in the complete absence of prophylaxis. The results: only three surgical site infections total, an overall rate of about one percent, cultured as Staphylococcus aureus in two cases and Klebsiella oxytoca in one, both treated successfully with a single oral antibiotic course. On univariate analysis, no factor reached significance except lifetime smoking history — all three infected patients had ever smoked, compared with under half of the noninfected group, and that difference was statistically significant, though obviously based on a numerator of just three events, so it's a fragile signal. Age, sex, body mass index, active smoking, diabetes, immunosuppression, anticoagulation, tumor type, number of Mohs stages, tumor size, and defect size all showed no significant association.

The authors are appropriately cautious given the small numerator, and they explicitly note the retrospective design likely underestimates the true infection rate, since not every minor wound issue necessarily gets documented or captured in a chart review. But the headline comparison — one percent here versus the eight and a half percent cited in the guideline that's driving current practice — is a meaningful contrast, and their bottom-line recommendation is that they do not advise routine prophylactic antibiotics for Mohs surgery with full-thickness lip wedge repair. Practically, this is a useful, if not definitive, data point to have in your back pocket: it won't singlehandedly overturn the 2008 advisory statement, but it adds real procedure-specific evidence that the historical eight-and-a-half-percent figure, generated from wedge excision rather than Mohs-staged surgery with careful margin control, may not apply to your practice, and it supports selectively reserving prophylaxis for patients with a smoking history rather than using it routinely across the board.

Last, and this one is genuinely practice-relevant — an advisory statement on the use of perioperative cephalexin in penicillin-allergic patients undergoing dermatologic surgery. This isn't a primary study; it's a literature review paired with expert consensus, prompted by a Mayo Clinic enterprise-wide policy shift toward using cefazolin first-line in penicillin-allergic patients, even those with a history of anaphylaxis. The authors did a structured PubMed search across several term combinations, screened everything for relevance, chased citations in seminal papers, and then brought the synthesized literature to a multidisciplinary panel — dermatologic surgeons, an infectious disease physician, an allergy and immunology physician, and a pharmacotherapy and infectious disease pharmacist — to reach final consensus recommendations. That's the right process for a question like this, where the primary literature is thin within dermatologic surgery specifically but extensive in general surgical and hospital-based literature.

The evidence they lay out is worth internalizing point by point. First, the scale of the mislabeling problem: something like ten to fifteen percent of the population carries a penicillin allergy label, but fewer than five percent of those labeled actually have a true, reproducible allergy on formal testing — most labels trace back to viral rashes, family history, or simple intolerances like nausea rather than true IgE-mediated hypersensitivity. Second, the mechanism of cross-reactivity has been substantially revised — it's not the shared beta-lactam ring that drives cross-reactivity, as was historically taught, but similarity of the R1 side chain, and only cephalexin and cefadroxil among common cephalosporins share an R1 side chain with the amino-penicillins, ampicillin and amoxicillin respectively. That means patients with a specific amino-penicillin allergy carry a modestly elevated cross-reactivity risk to cephalexin, while patients allergic to other penicillins — like dicloxacillin, nafcillin, oxacillin, or plain penicillin — essentially don't share that structural risk at all. Third, actual cross-reactivity rates are far lower than historically taught: contemporary estimates put cross-reactivity with first-generation cephalosporins around one percent rather than the old teaching of ten percent, and even in a rechallenge study of patients with documented allergy to ampicillin, cephalexin, or cefaclor, fewer than one in a hundred subsequent cephalexin courses provoked a new reaction. And fourth, penicillin allergy itself wanes over time — roughly ten percent of true allergy resolves per year, such that about eighty percent of patients test negative on skin testing after a decade.

The other half of the argument is about the alternatives you'd otherwise reach for. Clindamycin and vancomycin, the traditional substitutes in penicillin-allergic patients, carry their own significant downsides: penicillin-allergic patients given noncephalosporin alternatives have roughly a fifty percent higher surgical site infection rate in the broader surgical literature, clindamycin carries a dramatically elevated risk of Clostridioides difficile infection, and somewhat counterintuitively, clindamycin actually causes more hypersensitivity reactions overall than cefazolin does. The authors are honest that most of this comparative safety data comes from general and orthopedic surgery literature rather than dermatologic surgery specifically, so it's extrapolated rather than directly proven in our setting — a fair caveat to keep in mind rather than a fatal flaw.

Putting it together, the advisory statement's bottom line is that cephalexin should be used as the first-line perioperative prophylactic antibiotic in dermatologic surgery for patients with a documented penicillin allergy, including a history of anaphylaxis, with the caveat that patients with a specifically confirmed amino-penicillin allergy carry a somewhat higher, though still low, cross-reactivity risk. Worth noting the nuance that Mayo's own internal enterprise policy for higher-risk or anaphylaxis-history patients defaults to parenteral cefazolin rather than oral cephalexin specifically because cefazolin has a unique R1 side chain shared with no penicillin, but for routine outpatient dermatologic surgery prophylaxis, this statement supports cephalexin broadly. This is genuinely practice-changing guidance if you've been reflexively reaching for clindamycin every time you see a penicillin allergy label in the chart — the evidence here supports treating that as the exception rather than the rule, reserving alternatives for patients with a truly high-risk history, and otherwise proceeding with cephalexin.

That wraps up this issue. To summarize the actionable threads: fractional carbon dioxide laser is a reasonable adjunct for recalcitrant lichen simplex chronicus but not yet a first-line replacement for topical steroid; biopsy technique for suspected melanoma deserves renewed attention to adequate depth, since transection itself may not worsen prognosis but can trigger unnecessary sentinel node biopsies in thin tumors; routine antibiotic prophylaxis for Mohs surgery with full-thickness lip wedge repair looks hard to justify given a real-world infection rate near one percent; and perioperative cephalexin deserves to be your default, not your exception, in penicillin-allergic patients including those with prior anaphylaxis. Thanks for listening, and I'll see you next month.