Onychomycosis, or toenail fungus, is a widespread ailment affecting millions worldwide. It causes discolouration, thickening, and brittleness of the nails, often leading to discomfort and aesthetic concerns. Understanding the accurate diagnosis process is essential for timely and effective treatment.

What is toenail fungus?

Toenail fungus is a fungal infection that invades the keratin structure of nails. It can be caused by various types of fungi, including dermatophytes(Trichophyton rubrum), yeasts(such as Candida species), and non-dermatophyte moulds(including Fusarium, Aspergillus, and Scopulariopsis).¹ The infection typically begins at the edge of the nail and gradually spreads to the nail bed, resulting in visible and structural changes. When dermatophytes cause onychomycosis, this condition is called tinea unguium. 

How infection occurs

• The fungi infect the nail through openings or breaks in the nail or surrounding skin, thriving in warm, moist environments
• Dermatophytes grow on keratin in the nail and spread from athlete’s foot or direct contact with contaminated surfaces or objects

Common transmission routes

•  Contacting the skin/nail with infected individuals
• Sharing unsanitized nail grooming tools or towels
• Walking barefoot in warm, moist public places (showers, locker rooms, swimming pools)

Why accurate diagnosis matters

Correct diagnosis of toenail fungus is vital because several conditions mimic its symptoms, such as psoriasis, eczema, bacterial infections, and trauma-induced nail deformities. Misdiagnosis can lead to inappropriate treatments, prolonged discomfort, and unnecessary expenses.²

How to diagnose toenail fungus

Diagnosing toenail fungus involves a combination of clinical evaluation, laboratory tests, and imaging techniques. Below are the steps involved:

Clinical examination

A healthcare provider begins by visually inspecting the affected nail. Key features to look for include:

• Yellow, white, or brown discolouration
• Thickened or brittle nails
• Distorted nail shape
• Onycholysis (nail detachment from the bed)
• Foul odour in severe cases

The clinician may also review the patient’s medical history, lifestyle habits, and previous nail injuries.

Dermoscopy

Dermoscopy involves using a dermatoscope, a specialised magnifying tool, to examine the nail’s surface and substructure. This tool helps identify patterns consistent with fungal infections, such as longitudinal streaks and irregular pigmentation.

Microscopic examination (KOH Test)

The potassium hydroxide (KOH) test is a quick and cost-effective method for identifying fungal elements.³

• Nail scrapings are collected from the affected area
• The sample is treated with potassium hydroxide, which dissolves keratin and exposes fungal hyphae under the microscope
• The presence of branching filaments confirms a fungal infection
• They cannot specify species

Fungal culture

A fungal culture involves placing nail samples on a culture medium to promote fungal growth. This test helps identify the specific fungus responsible for the infection.⁴

• Samples are incubated for up to four weeks
• Positive cultures reveal colonies that can be further examined for fungal species identification

Periodic Acid-Schiff (PAS) Stain

A periodic acid-schiff (PAS) stain is a histopathological technique used on nail clippings.⁵

• The sample is embedded in paraffin and stained with PAS solution
• Fungal elements, including hyphae and spores, stain bright red, making them easily visible under a microscope
• This method is highly sensitive and often preferred for definitive diagnosis
• Molecular Techniques (PCR Testing)

Polymerase Chain Reaction (PCR) is a rapid and highly sensitive method for detecting fungal DNA.⁶

• PCR can identify multiple fungal species simultaneously
• It is beneficial in cases where conventional culture methods fail

Imaging techniques

In advanced or complicated cases, imaging techniques like X-rays or ultrasounds may be used to assess the extent of nail and bone involvement.⁷

Differential diagnosis

Since up to half of all dystrophic (abnormal) nails have non-fungal origins, it is necessary to differentiate onychomycosis, a toenail fungus, from several nail illnesses that share similar clinical symptoms. Hence, certain conditions can mimic toenail fungus, making differential diagnosis essential.²

• Psoriasis: Thickened nails with pitting. Nail psoriasis often also shows pitting, oil-drop/salmon patches, and may be associated with skin psoriasis elsewhere
• Eczema: Red, inflamed skin around the nail
• Lichen planus: Purple, flat-topped lesions around the nail. Causes nail dystrophy, longitudinal ridging, and thinning; sometimes all nails are affected (twenty-nail dystrophy)
• Bacterial infections: Green or black nail discolouration. Acute or chronic paronychia (inflammation/infection of nail folds) can also cause thickened or dystrophic nails
• Trauma: Nail thickening and discolouration without fungal involvement. Nail trauma can result in onycholysis and debris accumulation; the nail bed appears normal once the overlying nail is removed
• Onychogryphosis (Ram’s horn nail): Extreme nail thickening and curvature, sometimes from trauma, ageing, or circulation disorders
• Nail tumours: Tumours (benign or malignant, e.g., melanoma, Bowen’s disease, fibromas) can cause discoloration, thickening, or dystrophy mimicking fungal nail changes
• Other mimics: Irritant/contact dermatitis, pachyonychia congenita, yellow-nail syndrome, idiopathic onycholysis, and verruca (warts)

Home tests and their limitations

Some individuals attempt home remedies or visual assessments to diagnose toenail fungus. However, these methods are often unreliable and can lead to misdiagnosis. Seeking professional evaluation is always recommended.

Treatment options based on diagnosis

Once toenail fungus is accurately diagnosed, treatment options can be explored.^8,9 These include:

Topical antifungal medications

• Suitable for mild infections
• Examples: Ciclopirox, Efinaconazole

Oral antifungal medications

• Recommended for moderate to severe cases
• Examples: Terbinafine, Itraconazole
• Oral medications require liver function monitoring due to potential side effects

Laser therapy

• Targets fungal elements without damaging surrounding tissue
• Ideal for people who cannot tolerate oral drugs

Surgical nail removal

• Reserved for severe or recurrent cases
• Can be combined with antifungal treatment

Natural remedies

Tea tree oil, vinegar soaks, and other natural treatments may provide relief but lack robust clinical evidence.

Preventive measures

Prevention plays a crucial role in managing toenail fungus:

• Maintain proper foot hygiene
• Keep nails trimmed and clean
• Avoid walking barefoot in communal areas
• Wear breathable footwear and moisture-wicking socks
• Disinfect nail clippers and other grooming supplies

Complications of untreated toenail fungus

Ignoring toenail fungus can lead to several complications:

• Chronic pain and discomfort
• Secondary bacterial infections
• Permanent nail deformities
• The infection spread to additional nails and skin

When to see a doctor

Seek medical advice if:

• The nail becomes increasingly thickened or discoloured
• Pain or discomfort interferes with daily activities
• The infection spreads to other nails or skin
• There is a history of diabetes or compromised immune function

FAQs

How long does it take to diagnose toenail fungus?

The diagnostic process can vary. KOH tests provide immediate results, while fungal cultures may take up to four weeks.

Can toenail fungus disappear on its own?

In most cases, toenail fungus does not resolve without treatment and may worsen over time.

Is laser treatment effective for toenail fungus?

Laser treatment is effective and has minimal side effects, making it a good option for patients who cannot tolerate oral medications.

Can I use over-the-counter remedies for toenail fungus?

OTC treatments may be effective for mild cases but are generally less potent than prescription medications.

How can I prevent toenail fungus from recurring?

Maintain good foot hygiene, wear breathable shoes, and avoid walking barefoot in communal areas.

Summary

Accurate diagnosis of toenail fungus involves a combination of clinical examination, laboratory tests, and advanced diagnostic techniques. Early and precise identification allows for tailored treatment strategies, reducing the risk of complications and improving outcomes. Individuals can effectively manage and overcome toenail fungus by understanding the signs, seeking timely medical advice, and adhering to preventive measures.