17 - Onychomycosis

Question 1

Onychomycosis

Answer 1

Nail infection caused by any fungus

Question 2

Dermatophytes

Answer 2

Fungi that require keratin for growth which cause superficial infections of nails (and also skin and hair) in humans and in animals

Question 3

Tinea unguium

Answer 3

Clinical term for dermatophytic onychomycosis, three main forms:
o Distal subungual (90% of cases), Proximal subungual (3% of cases), White superficial (7% of cases)

Question 4

Epidemiology of onychomycosis

Answer 4

• Largest study of 15,000 Canadian patients presenting to dermatologist or PCP found 8% had onychomycosis
• Nearly all of these patients had toenail involvement alone

Question 5

Risk factors for onychomycosis

Answer 5

Main one = Older age

Question 6

Proximal subungual onychomycosis

Answer 6

• **THINK HIV **
• Uncommon
• Begins and progresses as does distal subungual onychomycosis
• Affects proximal portion of nail near the cuticle and extends distally
• Occurs in severely immunocompromised patients (should always prompt HIV testing)***
• KNOW THIS FOR A TEST QUESTION DO AN HIV TEST IF YOU SEE THIS

Question 7

Fungal melanoychia

Answer 7

General

• Uncommon (somewhat – but all of you will see this
• Also known as ungual phaeohyphomycosis
• Onychomycosis caused by fungal species capable of producing melanin (dematiaceous fungi)

This wasn’t the specific test question, just a background

Question 8

Appearance of fungal melanochyia clinically

Answer 8

• Brown-black discoloration of nail plate in diffuse, linear, or localized pattern +/- nail dystrophy
• CAN LOOK VERY DIFFERENT CLINICALLY

Question 9

Differential diagnosis of melanochyia

Answer 9

• **Differential Dx: Racial longitudinal melonynchia (benign) and MELANOMA***
• FIRST – DO A NAIL CLIPPING AND TEST FOR FUNGUS
• If it is not fungus, test for melanoma – do a real biopsy

TEST QUESTION***

Question 10

Best test for fungal nail infection

**TEST QUESTION

Answer 10

Histopathologic examination with PAS stain

• Results available in 24-48 hrs
• **Most sensitive and specific** KNOW THIS
• You can see HYPHAL structures – that is what you need to see to diagnose

Question 11

Treatment for onychomycosis

Answer 11

• Terbinafine is an allylamine and is primarily fungicidal. It is an inhibitor of CYP2D6
• Itraconazole and fluconazole are triazoles that are primarily fungistatic. They are inhibitors of CYP3A4 (more drug interactions, check meds).

Just background info (not test question)

Question 12

What is a dangerous side effect of all 3 medications for onychomycosis?

Answer 12

All three medications can cause HEPATOTOXICITY

• CHECK LIVER ENZYMES BEFORE STARTING
• Make sure the patient has an underlying healthy liver prior to starting
• The manufacturer of terbinafine recommends checking pretreatment serum aminotransferases and monitoring for potential symptoms of hepatotoxicity during treatment