Dermatology MCQ - Inflammatory Dermatoses - Juvenile plantar dermatosis

A 7-year-old boy is brought to the clinic by his mother due to a persistent, painful rash on the soles of his feet. The rash is worse in the winter and improves during the summer holidays. On examination, the skin on the forefeet and weight-bearing surfaces of the soles appears symmetrically glazed, erythematous, and hyperkeratotic, with deep fissures. The interdigital spaces are unaffected. What is the most likely diagnosis?

A. Tinea Pedis
B. Atopic Dermatitis
C. Psoriasis
D. Juvenile Plantar Dermatosis
E. Allergic Contact Dermatitis

Correct Answer: D. Juvenile Plantar Dermatosis

Explanation:

• The presentation is classic for Juvenile Plantar Dermatosis (JPD), also known as "sweaty sock dermatitis." The hallmark features include its location on the weight-bearing areas of the soles (balls of feet, heels, toes), the characteristic glazed, "patent-leather" or "glazed porcelain" appearance of the skin, and the presence of painful fissures. It is strongly associated with atopy and is exacerbated by the cycle of sweating in occlusive footwear followed by rapid drying, which leads to cracking of the stratum corneum.

• Why the other options are incorrect:

  • A. Tinea Pedis: This fungal infection is uncommon in young children. It typically presents with scaling, maceration, and erosions in the interdigital spaces (especially between the 4th and 5th toes), which are notably spared in this case. A potassium hydroxide (KOH) preparation would be positive.

  • B. Atopic Dermatitis: While this patient may have an atopic background, classic atopic dermatitis on the feet tends to be more widespread, pruritic, and lichenified, often affecting the dorsa of the feet rather than the specific, symmetric, glazed appearance of the plantar surfaces seen in JPD.

  • C. Psoriasis: Plantar psoriasis presents as well-demarcated, thick, silvery-scaly plaques, often with painful pustules in the case of palmoplantar pustulosis. The diffuse, glazed erythema and fissuring described is not typical of psoriasis.

  • E. Allergic Contact Dermatitis: This would present with a more acute, intensely pruritic, and vesicular eruption. Its distribution would correspond to contact with an allergen (e.g., from shoes). The chronic, symmetric, and glazed appearance is not characteristic.

Key Points for Exams

• Epidemiology: Most common in children aged 3-14 years, with a peak between 4 and 8 years. There is a strong association with atopy.

• Pathophysiology: Thought to be caused by repeated cycles of hydration (from sweating) and dehydration of the plantar skin, exacerbated by friction from synthetic socks and occlusive footwear. This leads to a disruption of the epidermal barrier.

• Clinical Course: The condition is chronic and relapsing but has an excellent prognosis for spontaneous resolution by adolescence.

• Management: The mainstay is conservative, non-pharmacological measures:

  1. Footwear Modification: Encourage wearing leather-soled shoes and cotton or wool socks to absorb moisture and reduce friction. Avoid occlusive synthetic footwear.

  2. Emollients: Frequent application of thick, occlusive emollients (e.g., petrolatum, lanolin) throughout the day, especially after removing shoes and socks, is crucial to repair the skin barrier.

  3. Avoid Irritants: Reduce frequency of washing feet with soap, which can be drying.

  4. Topical Therapy: For inflamed or fissured areas, a short course of a medium-potency topical corticosteroid can be used to reduce inflammation and pain. Ointment-based formulations are preferred.