Scaly Rashes of the Feet: Could It Be Fungal?

R. Vender, MD, FRCPC

Faculty of Medicine, McMaster University, Hamilton, Ontario, Canada

This article will deal with the diagnosis and treatment of common eruptions on the feet. These conditions include:

Useful tests include:

• KOH (Potassium hydroxide) exam of scale for fungus from skin and nail
• Use a No. 15 blade and gently scrape scale from the edge of
  the plaques into the black transport paper, usually supplied by a diagnostic lab.
• Bacteriology culture swab
• Patch testing

Tinea Pedis (Skin and Nail)

• One of the most common dermatologic conditions
• Seen more often in men
• Almost always involves the lateral web spaces
• Soles involved and may spread onto the dorsal aspects, usually asymmetrically
• Nail involvement may follow from a skin infection or vice versa
• Cracking of the skin may create an entry site for bacterial infection producing secondary cellulitis
• Often asymptomatic but can be itchy
• Feet may be malodorous
• Painful if fissured

Tests

• KOH examination from the skin, subungual debris, or nail clippings confirms the diagnosis.
• Culture determines specific name of fungus. Check the dry scale or roof of blister. May be negative if significant inflammation.

Clinical Subtypes

• Web-space scaling and maceration. May have significant bacterial colonization.
• Dry type. Scaling can involve skin creases or the whole sole that has a powdery scale (moccasin type).
• Acute blistering. Small blisters often on instep
• Soggy white skin changes with cracking
• Nails can become involved and act as a reservoir for reinfection.

Treatment

• General measures, such as changes in footware to reduce heat and sweating
• Wear cotton or absorbent socks.
• Relapses are very common with any type of tinea infection of the feet, so intermittent maintenance using topical antifungals should be considered after clearance has been achieved.
• Antifungal powders are only of value as prophylaxis.

Topical Therapy for Tinea Pedis

Oral Therapy for Tinea Pedis

Tinea pedis

• Confirm with KOH and culture first.
• Terbinafine 250mg daily for 2 weeks
• Itraconazole (Sporanox®) studies suggest 400mg daily for 1 week or 100-200mg daily for 2-4weeks.
• Studies comparing these two drugs and using itraconazole at 100mg showed terbinafine to be much more effective.
• However, it is now known that a higher dose of itraconazole is required.
• Monitor appropriate blood work.

Nail

• Confirm with KOH and culture first and monitor appropriate blood work, i.e., CBC and LFTsat baseline and at 1 month.
• Ciclopirox 8% nail lacquer is effective in the milder forms of nail infection. Mycological cures in the range of 52% can be achieved.
• Adding ciclopirox 8% nail lacquer to terbinafine significantly increases cure rates.
• Terbinafine is thought to be the treatment of choice at a dose of 250mg daily for 3 months. Using this drug for 1 week every month for 3 or 4 cycles is almost as effective, reducing both costs and worries about side-effects.

Dyshidrotic Eczema (Pompholyx)

• A recurrent eruption affecting hands and feet seen mostly in young adults
• Associated with atopy, hyperhidrosis, stress and an allergic contact dermatitis
• Acute
• Intensely itchy
• Tiny blisters, which may become multilocular on soles and toes
• Less commonly found in the web spaces
• If pustules are present, swab for bacterial infection such as Staphylococcus.
• Once the blisters settle there may be a dry, chronic, scaly, fissured rash.

Treatment

• Acute
  • Compress blisters with saline, tap water, or 10% aluminum acetate for 20 minutes q.i.d. Large blisters can be drained.
  • Moderate-to-high potency topical steroid creams should be used after compressing.
  • Studies show that immunomodulators, such as pimecrolimus (Elidel®) and tacrolimus (Protopic®), could be added with benefit.
  • Use oral antibiotics if there is a suspicion of bacterial infection, such as Staphylococcus or Streptococcus.
  • Oral antihistamines can help with itch (sedation).
  • In severe cases, oral prednisone (Deltasone®) for approximately 2 weeks should be utilized.
• Chronic
  • Change to moderate-to-high potency topical steroid ointment rather than cream.
  • Using a topical corticosteroid intermittently, such as on weekends only, and using topical immunomodulators on weekdays has been reported.

Juvenile Plantar Dermatosis

• • Seen in childhood up to the age of 15
  • A tender, glazed erythema on the weight-bearing forefoot and toes

Nonscaly and sometimes fissured

• No vesicles are observed
• Worsened by sweating; may be caused by alternating sweating and drying as experienced by those who wear ‘sneakers’.
• Rule out fungus by KOH exam.
• 10% are patch test positive.

Treatment

• Minimize occlusive foot wear; change to cotton or absorptive socks.
• Mild topical steroid ointments b.i.d.
• Emollients such as petroleum jelly can be helpful.
• Occlusive ointments such as zinc paste can help some.
• Tar ointments have been reported as useful (e.g., 10% LCD in hydrophilic petrolatum).

Pustular Psoriasis of the Palms and Soles

• Creamy yellow, sterile pustules on an erythematous base
• The lesions are at different stages, and the pustules mature into a brown color and then become scaly
• 30% of patients have psoriasis elsewhere
• In children, especially infants, vesicopustules on the soles could suggest scabies.

Treatment

• Mild disease can be controlled with medium-to-potent topical steroids.
• Long-term risk of atrophy. Some may respond to calcipotriol combined with a corticosteroid (Dovobet®).
• Topical UVB/PUVA is useful in some patients.
• Acitretin (Soriatane®) or methotrexate (Trexall®) for resistant disease

Contact Dermatitis

• Although irritant dermatitis can be seen, allergic contact is a more significant problem.
• Itchy eczematous dermatitis on the dorsal aspect of the feet raises the possibility of a contact dermatitis, especially to footwear.
• The rash may be well defined at the area of contact, e.g., shoe tongue. The condition worsens with conditions that increase sweating, and in the summer months.

Treatment

• Identify and avoid the allergen.
• Patch testing is a must if there is clinical suspicion.
• Topical corticosteroids are the treatment of choice, but will not clear the condition if the allergen contact is still present.