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Onychomycosis (Fungal Nail Infection) – A High-Yield Clinical Guide for PLAB 2


What is Onychomycosis?

Onychomycosis is a fungal infection affecting the nail plate, nail bed, or surrounding structures.

It most commonly affects the toenails.



Causative Organisms


Dermatophytes (Most common and exam-important)

These are the commonest causative organisms in onychomycosis.

Main organisms include:

  • Trichophyton rubrum (most common)

  • Trichophyton interdigitale


Yeasts

Examples include:

  • Candida species

Yeast infections are more commonly associated with:

  • Fingernail involvement

  • Chronic wet work

  • Immunosuppression


Non-dermatophyte moulds

Less common causes include environmental moulds.

These may sometimes represent contamination rather than true infection, so clinical correlation is important.



Common Clinical Features

Patients may present with:

  • Thickened nails

  • Yellow, white, or brown discoloration

  • Brittle or crumbly nails

  • Nail deformity

  • Nail separation from the nail bed (onycholysis)

  • Debris under the nail



Risk Factors

Important risk factors include:


Medical conditions

  • Diabetes mellitus

  • Peripheral vascular disease

  • Immunosuppression

  • Psoriasis

  • Increasing age


Environmental and lifestyle factors

  • Excessive sweating

  • Tight or occlusive footwear

  • Humid environments

  • Poor foot hygiene

  • Communal showers/swimming pools

  • Repeated nail trauma


Associated fungal infection

  • Concurrent Tinea pedis is one of the most important risk factors.



Diagnosis


Why confirmation is important

Not all abnormal nails are fungal infections.

Conditions such as:

  • Psoriasis

  • Trauma

  • Eczema

  • Lichen planus

can mimic fungal nail disease.

Because oral antifungals require prolonged treatment and may cause side effects, diagnosis is usually confirmed before starting treatment.


Samples Taken

Samples may include:

  • Nail clippings

  • Nail scrapings

  • Subungual debris (material from under the nail)

These are sent for:

  • Microscopy

  • Fungal culture

  • PCR testing (in some centres)


Important point

Samples should ideally be taken:

  • Before starting antifungal treatment



Why Topical Treatment Alone Often Fails

Although this is a fungal infection, the fungus often lies deep under the nail plate.

The nail acts like a hard barrier, making it difficult for topical medications to penetrate effectively.

This is why topical treatment:

  • Requires prolonged use

  • Has lower cure rates

  • Has higher recurrence rates

Oral medications reach the nail through the bloodstream and are therefore often more effective.


When Topical Treatment is Appropriate

Topical treatment can be considered if:

  • ≤50% of the nail is affected

  • ≤2 nails are affected

  • No nail matrix involvement

  • Superficial white onychomycosis


Topical Treatment


  • Amorolfine 5% nail lacquer

    • Typical duration:

      • Fingernails: ~6 months

      • Toenails: ~9–12 months

    • Another option:

      • Ciclopirox


Oral Treatment

  • Terbinafine: Usually first-line treatment for dermatophyte infections.

    • Typical duration:

      • Fingernails: ~6 weeks

      • Toenails: ~12 weeks

  • Itraconazole

    • Used when terbinafine is unsuitable or for some non-dermatophyte infections.


When Oral Treatment is Preferred

Oral therapy is usually preferred if:

  • Multiple nails are affected

  • Toenails are extensively involved

  • Nails are thickened or dystrophic

  • Matrix involvement is present

  • Topical treatment has failed



Blood Tests Before Oral Treatment

Before starting oral antifungals such as terbinafine or itraconazole:

  • Baseline liver function tests (LFTs) are commonly recommended

This is because these medications can rarely cause liver toxicity.

Patients should seek medical attention if they develop:

  • Jaundice

  • Dark urine

  • Severe nausea/vomiting

  • Abdominal pain

  • Significant fatigue



Important Counselling Points

Patients should be informed that:

  • Nail growth is slow

  • Improvement takes time

Even after successful treatment:

  • Fingernails may take ~6 months to normalize

  • Toenails may take 12–18 months

Recurrence is common if risk factors persist.



Advice to Reduce Recurrence

  • Treat concurrent athlete’s foot

  • Keep feet dry

  • Change socks regularly

  • Avoid tight footwear

  • Avoid sharing nail clippers/shoes

  • Wear footwear in communal showers and pools



High-Yield Clinical Summary


Mild disease

→ Topical treatment may be sufficient

Extensive disease or matrix involvement

→ Oral antifungal treatment usually required

Before oral treatment

→ Confirm diagnosis and check baseline LFTs



📚 References

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