Hydroxychloroquine

證據等級: L5

預測適應症: 10 個

Hydroxychloroquine: From Autoimmune Diseases to Quinquaud's Folliculitis Decalvans

One-Sentence Summary

Hydroxychloroquine (HCQ) is an established antimalarial and immunomodulatory agent widely used internationally for systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and malaria prevention, though it is currently not registered in Singapore. The TxGNN model predicts it may be effective for Quinquaud's Folliculitis Decalvans — the most common primary neutrophilic scarring alopecia — with no registered clinical trials and 4 publications supporting this direction. Critically, the 2025 EADV Task Force on Hair Diseases has already incorporated HCQ as a formal adjuvant treatment option, grounding the prediction in expert clinical consensus.

Quick Overview

Item	Content
Original Indication	Not registered in Singapore; internationally used for malaria, SLE, and rheumatoid arthritis
Predicted New Indication	Quinquaud's Folliculitis Decalvans
TxGNN Prediction Score	98.66%
Evidence Level	L3 (Observational study + Expert Consensus)
Singapore Market Status	✗ Not marketed
Number of Registrations	0
Recommended Decision	Research Question

Why is This Prediction Reasonable?

Hydroxychloroquine belongs to the 4-aminoquinoline antimalarial class. Although formal MOA data is not available in this evidence pack, HCQ's anti-inflammatory mechanism is well established in clinical literature: it inhibits endosomal Toll-like receptor (TLR7/9) signalling and lysosomal acidification, thereby disrupting antigen presentation and suppressing downstream production of key inflammatory mediators — particularly IFN-γ, IL-1β, IL-6, and IL-17. These properties make HCQ a broad-spectrum immunomodulator with proven clinical utility across autoimmune and inflammatory conditions.

Quinquaud's folliculitis decalvans (FD) is a chronic, relapsing scarring alopecia driven primarily by neutrophilic infiltration of hair follicles. While Staphylococcus aureus colonisation has historically been implicated in its pathogenesis, an emerging body of evidence recognises a subset of patients with "lichen planopilaris-like" FD in which immune dysregulation — characterised by IL-1β/IL-17 axis activation and neutrophil-dominated follicular inflammation — plays the central pathogenic role. This mechanistic overlap with HCQ's TLR-inhibitory and cytokine-suppressive targets provides a direct and biologically plausible rationale for the TxGNN prediction.

The prediction is further supported by real-world clinical data: the 2025 EADV Task Force on Hair Diseases position statement (PMID 40230058) formally endorsed HCQ as an adjuvant treatment option for FD, and a dedicated 5-year retrospective cohort study (PMID 39340420, n=49) demonstrated clinical benefit in patients with immune-predominant FD phenotypes. This suggests the TxGNN model has correctly identified an emerging clinical niche, even in the absence of prospective controlled trial data.

Clinical Trial Evidence

Currently no related clinical trials registered.

Literature Evidence

PMID	Year	Type	Journal	Key Findings
40230058	2025	Expert Consensus (EADV Position Statement)	J Eur Acad Dermatol Venereol	EADV Task Force on Hair Diseases formal position statement on FD management; HCQ endorsed as an adjuvant option to control inflammation and prevent further hair loss
39893632	2025	Comprehensive Review	Expert Opin Drug Metab Toxicol	Systematic review of alopecia therapies (PubMed/MEDLINE, Embase, Cochrane, 2015–2024); covers both scarring and non-scarring types, including current FD treatment landscape
39340420	2025	Retrospective Cohort (5-year, n=49)	Clin Exp Dermatol	Direct evidence: HCQ as adjuvant therapy for FD; demonstrates clinical benefit particularly in patients with less-active or "lichen planopilaris-like" FD phenotypes, supporting the immune-mediated subtype hypothesis
32030059	2019	Case Report	Int J Trichology	Therapy-recalcitrant FD ultimately controlled with adalimumab; HCQ listed among prior treatment attempts, contextualising its role before biological escalation

Singapore Market Information

Hydroxychloroquine is currently not registered in Singapore. No product authorisations are on record with HSA.

Safety Considerations

Please refer to the package insert for safety information.

Summary of All Predicted Indications

The TxGNN model identified 10 high-scoring repurposing candidates for Hydroxychloroquine spanning hair disorders and rheumatic diseases. Evidence strength and clinical recommendations vary substantially across predictions:

Rank	Disease	TxGNN Score	Evidence Level	Recommendation	Key Evidence Basis
1	Quinquaud's Folliculitis Decalvans	98.66%	L3	Research Question	EADV 2025 position statement; 5-year retrospective cohort (n=49)
2	Telogen Effluvium	98.55%	L5	Hold	1 indirect case series (COVID-19 sequelae); no mechanistic link to HCQ
3	Alopecia Antibody Deficiency	98.53%	L5	Hold	1 highly indirect case report (SLE+HAE); no direct evidence
4	Alopecia Mucinosa	98.47%	L3	Research Question	2 case series + 2 case reports with direct HCQ use for follicular mucinosis
5	Hereditary Hypotrichosis with Recurrent Skin Vesicles	98.40%	L5	Hold	No literature; genetic aetiology with no immunologic rationale
6	Alopecia-Intellectual Disability-Hypergonadotropic Hypogonadism Syndrome	98.37%	L5	Hold	No literature; rare multi-system genetic syndrome
7	Alopecia Areata	98.21%	L3	Research Question	1 Phase 4 open-label trial (n=16, completed); mixed retrospective data; NEGATIVE result for alopecia totalis (PMID 27051848)
8	RF+ Polyarticular Juvenile Idiopathic Arthritis	98.04%	L4	Research Question	1 indirect case report; high mechanistic plausibility via HCQ's adult RA indication
9	Juvenile Chronic Polyarthritis	97.75%	L3	✓ Proceed with Guardrails	Multiple systematic reviews; dedicated paediatric safety data (PMID 33548956); EULAR/ACR-endorsed csDMARD
10	Rheumatoid Nodulosis	97.75%	L4	Research Question	1 early case series (1993, PMID 8496880) reporting possible HCQ reversal of MTX-induced accelerated nodulosis

Important note: Rank 9 (Juvenile Chronic Polyarthritis) carries the strongest actionable recommendation ("Proceed with Guardrails"), supported by multiple systematic reviews, paediatric-specific safety data, and guideline endorsement — despite ranking lower by TxGNN score. A separate expedited evaluation for this indication is recommended.

Conclusion and Next Steps

Decision: Research Question

Rationale: For the top-ranked indication (Quinquaud's Folliculitis Decalvans), Level 3 evidence exists — including a 2025 EADV expert consensus and a 5-year retrospective cohort study — supporting HCQ as adjuvant therapy in immune-predominant phenotypes. However, the absence of any registered clinical trials, the lack of Singapore product registration, and unresolved formal safety data prevent advancement beyond a structured research question at this stage.

To proceed, the following is needed:

Regulatory pathway: Assess HSA special access scheme or expedited registration pathway for HCQ in Singapore, given the complete absence of current market authorisation
Formal safety review: Obtain and parse the original package insert (EMA/FDA) for key warnings and contraindications — particularly mandatory retinal toxicity screening (ophthalmologic monitoring schedule) and QTc prolongation risk
MOA data: Retrieve full mechanism of action from DrugBank API (DB01611) to complete the mechanistic justification
Study design: Develop a protocol for a Phase 2 pilot RCT specifically enrolling patients with immune-predominant ("lichen planopilaris-like") FD phenotypes, with standardised outcome measures (e.g., Folliculitis Decalvans Activity and Severity Index)
Parallel fast-track for Rank 9: Juvenile Chronic Polyarthritis should be evaluated under a separate, expedited review track given EULAR/ACR guideline support and available paediatric safety data

Disclaimer: This report is intended for research reference only and does not constitute medical advice. All drug repurposing candidates require rigorous clinical validation before any therapeutic application.

Disclaimer

This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.