Alopecia Severity Endpoints for Clinical Trials

The AI scoring provided by Legit.Health delivers automated, standardised alopecia severity scoring for clinical trials, quantifying scalp hair loss percentage across four quadrants and producing a SALT-aligned severity score: the endpoint recommended by FDA guidance for establishing alopecia areata treatment effectiveness.

FDA guidance context

The FDA’s guidance document Alopecia Areata: Developing Drugs for Treatment. Guidance for Industry. (2022) establishes the standard for clinical trial endpoints:

The SALT score is an acceptable efficacy measure for clinical trials evaluating treatments for alopecia areata.
A SALT score of 0 or 1 (0–1% scalp hair loss) at study end is a reasonable responder definition for patients with extensive hair loss.
Trials should use validated patient-reported outcomes to capture the patient perspective on hair loss severity.
Photographic documentation should follow a standardised protocol to ensure consistency across sites and visits.

Endpoint capabilities

The AI provides four distinct endpoints, each configurable per study protocol:

Endpoint	Definition	AI output	Typical use in protocol
Total ASALT score	Automated SALT score estimating the percentage of scalp affected by hair loss	0–100 continuous scale	Co-primary
Regional ASALT scores	ASALT score for each scalp quadrant (left, right, top, back)	0–100 per region	Secondary
SALT response categories	Responder analysis based on SALT change thresholds (SALT 50, SALT 75, SALT 90, SALT 100)	Binary response per threshold	Co-primary
Severity classification	Categorical severity based on total ASALT score (None, Limited, Moderate, Severe, Very Severe)	Category label and numeric severity	Secondary

Why SALT for alopecia trials?

The SALT score (Severity of Alopecia Tool) is the accepted standard for quantifying alopecia areata severity in clinical trials. It measures the percentage of scalp affected by hair loss on a 0–100 scale, where 0 means no hair loss and 100 means complete hair loss. FDA guidance explicitly recognises SALT as an acceptable efficacy measure, and responder definitions based on SALT thresholds (SALT 50, SALT 75, SALT 90, SALT 100) are standard primary endpoints. The ASALT (Automatic SALT) score automates this assessment from standardised photographs, eliminating the subjectivity inherent in visual percentage estimation.

How the AI works

The scoring pipeline processes each set of four scalp photographs in two stages:

Stage 1: Scalp segmentation

A deep learning segmentation model analyses each scalp quadrant image to identify hair-bearing and non-hair-bearing regions at the pixel level. The model produces a probability map for each pixel, which is then thresholded to classify scalp regions as having or lacking hair coverage.

AI segmentation showing hair-bearing and non-hair-bearing scalp regions — Hair loss segmentation: the AI identifies hair-bearing (green overlay) and non-hair-bearing (red overlay) regions to compute the percentage of scalp affected.

Stage 2: SALT score computation

The regional hair loss percentages are combined into a total SALT score using the standard anatomical weights:

\text{SALT} = \sum_{r \in \{\text{left}, \text{right}, \text{top}, \text{back}\}} w_r \cdot S_r

where $S_r$ is the percentage of hair loss in region $r$ and $w_r$ is the weight for that region (left 18%, right 18%, top 40%, back 24%), reflecting each quadrant's proportion of total scalp area.

SALT score	Severity	Clinical description
0	None	No detectable hair loss
1	Limited	1–24% scalp hair loss; localised patches
2	Moderate	25–49% scalp hair loss; multiple or larger patches
3	Severe	50–74% scalp hair loss; extensive involvement
4	Very Severe	75–100% scalp hair loss; near-total (alopecia totalis) or total loss

Visual report

The AI produces a structured severity report for each assessment, showing per-quadrant scores and the global ASALT score:

Protocol flexibility

The imaging and scoring protocol adapts to your study's needs. Legit.Health works with sponsors and CROs to configure the optimal protocol during study setup.

Imaging perspectives

Protocol	Perspectives	Use case
Standard 4-quadrant	4 views: Left side of scalp, Right side of scalp, Top of scalp, Back of scalp	Standard SALT protocol capturing all four scalp quadrants. Provides full scalp coverage for total SALT score calculation. Patient must be seated for the top perspective.
Custom	Any combination of perspectives	Any combination of scalp perspectives, defined in collaboration with the sponsor during protocol design. Can include additional close-up views for detailed lesion tracking.

Global score aggregation

Unlike acne or psoriasis (which use maximum or weighted component scores), SALT uses a single standard aggregation: the weighted sum of regional hair loss percentages. This is inherent to the SALT methodology and ensures comparability with established SALT literature.

Method	Formula	When to use
Weighted sum (SALT standard) (default)	$\text{SALT} = 0.18 \cdot S_{\text{left}} + 0.18 \cdot S_{\text{right}} + 0.40 \cdot S_{\text{top}} + 0.24 \cdot S_{\text{back}}$	Standard SALT aggregation. Each quadrant's hair loss percentage is weighted by its anatomical proportion of total scalp area. This is the only aggregation method used for SALT.

SALT response thresholds

In addition to the continuous SALT score, the system computes standard SALT response categories used as responder endpoints in registration trials:

Response	Definition	Clinical meaning
SALT 50	>=50% reduction from baseline SALT score	Clinically meaningful improvement
SALT 75	>=75% reduction from baseline SALT score	Substantial improvement
SALT 90	>=90% reduction from baseline SALT score	Near-complete regrowth
SALT 100	SALT score of 0 (complete regrowth)	Complete response

Use case: severity assessment and adverse event monitoring

While ASALT was first deployed in a clinical trial for adverse event monitoring (detecting drug-induced alopecia in a Phase 3 MASH trial), the primary use case for sponsors is severity measurement in alopecia areata treatment trials:

Efficacy endpoint: SALT score as co-primary or secondary endpoint for hair regrowth
Responder analysis: Automated SALT 50/75/90/100 classification at each visit
Longitudinal tracking: Severity evolution over the course of treatment
Safety monitoring: Automated alerts when hair loss exceeds a configurable threshold from baseline (e.g., >=25% increase)

The same technology serves both use cases with identical scoring methodology.

Alopecia Severity Endpoints for Clinical Trials

FDA guidance context

Endpoint capabilities

How the AI works

Stage 1: Scalp segmentation

Stage 2: SALT score computation

Visual report

Protocol flexibility

Imaging perspectives

Global score aggregation

SALT response thresholds

Use case: severity assessment and adverse event monitoring

Further reading

Scoring Methodology

Imaging Protocol

Clinical Evidence

Trial Workflow

Publications

FDA guidance context​

Endpoint capabilities​

How the AI works​

Stage 1: Scalp segmentation​

Stage 2: SALT score computation​

Visual report​

Protocol flexibility​

Imaging perspectives​

Global score aggregation​

SALT response thresholds​

Use case: severity assessment and adverse event monitoring​

Further reading​

Scoring Methodology

Imaging Protocol

Clinical Evidence

Trial Workflow

Publications

FDA guidance context

Endpoint capabilities

How the AI works

Stage 1: Scalp segmentation

Stage 2: SALT score computation

Visual report

Protocol flexibility

Imaging perspectives

Global score aggregation

SALT response thresholds

Use case: severity assessment and adverse event monitoring

Further reading