Which trichoscopic patterns distinguish the common non-scarring alopecias from one another?

Most examiners reach for one striking finding and stop there, and that's exactly where the reading goes wrong. Under the lens you're answering three questions at once: what the shafts look like, what's sitting in and around the follicular openings, and what the background shows. Get those three right and the common non-scarring diagnoses separate cleanly, because you're weighing a whole field instead of hunting a single sign.

• Androgenetic alopecia: Shaft diameter diversity above roughly 20 percent, single-hair units rising, occiput preserved.
• Alopecia areata: Evenly spaced yellow dots, with black dots and exclamation marks at the advancing margin.
• Telogen effluvium: Uniform calibre, no dots, only short upright regrowth and slightly more empty openings.
• Mechanical loss: Broken hairs of wildly uneven length, flame and tulip hairs, hair powder.

Which trichoscopic features are diagnostic of androgenetic alopecia, and why does hair shaft diameter diversity anchor the diagnosis?

Diameter diversity is the one finding that images the disease mechanism rather than its aftermath. Androgen-sensitive follicles don't switch off in a single step, so each cycle hands back a shorter, thinner, less pigmented shaft until terminal, intermediate, and vellus hairs sit side by side in the same field. That's why the occipital reference field matters so much: androgen-insensitive scalp examined minutes later gives you the ruler that makes a subtle diversity obvious.

What does alopecia areata look like under trichoscopy across its active, stable, and regrowing phases?

Trichoscopy earns its keep in alopecia areata by grading activity, not by confirming what you can already see. Read the phase right and you'll know whether to escalate, hold, or reassure, weeks before the patch looks any different clinically.

1. Active margin: Exclamation mark hairs a millimetre or two long that taper toward the scalp, alongside black dots and tapering broken hairs, all clustered at the advancing edge. A field rich in both predicts poor short-term regrowth and drives escalation more than patch diameter does.
2. Stable patch: Round or polycyclic yellow dots, densely and fairly evenly spaced across the whole patch and filled with degenerated keratin and sebum. In an otherwise quiet patch they mean the follicles are dormant, not destroyed.
3. Recovery: Short upright regrowing hairs of even length standing perpendicular to the scalp, often unpigmented at first, with coiled and pigtail hairs beside them.
4. Long quiescent: Empty openings, no dots, no dystrophic shafts, and a slower response to whatever you start.

How can telogen effluvium be recognised on trichoscopy when there is no focal patch to examine?

Telogen effluvium is the diagnosis you make out of what isn't there. The follicles are structurally normal, so the lens hands you normal architecture and nothing else, which feels like a failed examination until you realise that's the finding. Your real work here is negative work: proving no miniaturisation is hiding underneath the shed.

• Normal architecture: Uniform shaft calibre, no dots, no tapered or dystrophic shafts, normal background.
• Short upright regrowth: Even-length hairs spread over the whole scalp rather than confined to a patch.
• Empty openings: A modest rise, meaningful only when recounted at the same marked sites over months.
• Occipital comparison: Frontal and vertex calibre checked against the occiput to rule out hidden miniaturisation.

Which findings distinguish traction alopecia and trichotillomania from spontaneous shedding?

Mechanical hair loss gives itself away through irregularity. A shed drops whole shafts from their roots and leaves the rest intact, so lengths stay even; force snaps shafts wherever they happen to be weakest, and the field fills with broken ends of every conceivable length, none of them tapered.

Why does the same dot finding mean different things in different alopecias?

A dot is a hole seen end-on, and its colour only tells you what's filling it. The same yellow dot shows up in alopecia areata, in advanced pattern loss, and in dissecting conditions, so the dot on its own can never name a disease. What carries the information is density, arrangement, and the shafts sitting around it.

What confirms that follicular openings are preserved, and why does that finding rule out a scarring process?

This is the observation the whole comparison rests on, so make it deliberately instead of assuming it. A preserved ostium is a small round depression in the scalp surface, visible whether or not a shaft is emerging from it, and in normal scalp those depressions sit in a regular mosaic with units grouped in twos and threes. Lose them and the stem cell reservoir and canal have gone with them, which is why a missed scarring diagnosis costs follicles permanently while a missed non-scarring one only costs time.

• Preserved: Round depressions in a regular mosaic, units in twos and threes, however bald the area looks.
• Destroyed: A smooth, featureless, ivory-white surface with no mosaic and no depressions.
• Active edge signs: Perifollicular scale collaring the shaft, perifollicular erythema, or tufting of several shafts through one opening.
• The classic trap: Early frontal fibrosing alopecia, with a lonely hair in an emptied band, absent vellus hairs, and eyebrow loss.

Which magnification, lighting, and technique choices change what the examiner sees?

Technique decides which findings exist at all. If you only ever use one lighting mode you'll systematically under-report half of what's on that scalp, and you'll never know you did it. Magnification works the same way: 20 times is fine for distribution and dots, but grading calibre at that setting is guesswork.

Where does trichoscopy mislead, and which overlaps most often cause misdiagnosis?

The error that catches people out isn't misreading a finding, it's stopping once a plausible one turns up. Pattern loss and a shed coexist constantly, and it's the shed that brings the patient through the door. Confirm one, stop there, and you'll either chase a hairline while the ferritin sits on the floor, or reassure someone whose hairline is quietly receding.

How should trichoscopic findings be combined with pull tests, history, and biopsy?

Trichoscopy is a middle step, not a verdict. Take the history first and you walk to the lens with the field already narrowed, which is what turns an ambiguous image into a confirmatory one.

1. Timeline first: Ask about illness, surgery, delivery, weight loss, or a new medication in the one to six months before the shedding began, most often around three, plus family pattern, styling practice, and the age thinning was first noticed.
2. Read every field: Frontal, vertex, both temples, and the occiput, regardless of where the patient points.
3. Pull test: Grasp roughly 50 to 60 hairs and draw them along their length; more than about 6 coming away indicates ongoing shedding, and the extracted roots are worth examining for club-shaped telogen, tapered anagen, or dystrophic shafts.
4. Site the biopsy: Use the lens to find the active margin carrying scale, erythema, or tufting, then take a 4 mm punch parallel to the shafts and process it for horizontal sections.
5. Let the picture pick the bloods: A shed with normal architecture justifies ferritin, full blood count, thyroid function, and vitamin D; an areata picture justifies thyroid antibodies and a low threshold for screening other autoimmune disease.
6. Follow up at the biological interval: A few weeks to judge whether an areata patch is responding, at least six months before pronouncing on pattern loss treatment, with the same photographic fields both times.