Key Insights On Treating Plantar Psoriasis

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Author(s): 
Myron A. Bodman, DPM

   Finally, the rare differential condition could be arsenical keratosis of the palms and soles. One could investigate this differential diagnosis by exploring the patient’s travel history and possible exposure to well water contaminated with arsenic. In these cases, laboratory investigation could reveal hemolysis or electrolyte disturbances.

A Guide To Initial Treatment

The initial management should focus on symptom relief and the most likely scenario of psoriasis pending results of the workup of the differential diagnosis. For this patient, the painful, deep fissures limiting walking were the primary issue and initial treatment in the office consisted of lidocaine ointment to allow debridement and flattening of the vertical edges of the sole splits with a wetting agent and tissue nippers. In order to relieve the weightbearing pain, I applied loose Unna paste gauze dressings to the feet for 48 hours. At home, the patient applied triamcinolone 0.5% ointment twice daily followed by urea 40% cream at night. Once the fissures healed and the plaques thinned, the concurrent onychomycosis had cleared with an 84-day course of oral terbinafine (Lamisil, Novartis).

   The clinical diagnosis of psoriasis relies on searching for the essential disease characteristics. Most hyperkeratosis of the soles, which is due to excessive intermittent pressure as in tylomas, corns and calluses, is relatively clear and translucent while psoriatic hyperkeratosis is commonly opaque and white to yellow. Accelerated psoriatic keratinization produces the opaque hyperkeratosis of psoriasis. Accumulated immature keratinocytes retain their nuclei and therefore are not translucent like the more mature keratin of pressure keratoses.

   The prevalence of onychomycosis is actually higher in patients with psoriasis. Eighteen percent of patients with lower extremity psoriasis have concurrent onychomycosis.1 When it comes to moderate to severe onychomycosis, oral terbinafine is the drug of choice with long-term topical antifungal prophylaxis against re-infection.

   Another symptom of plantar psoriasis is increased sole temperature. Although there is no single normal foot temperature, sole temperatures do vary within a daily circadian rhythm between morning vasodilation and a cooler vasoconstricted state. Clinical examination usually occurs in a cool examination room when anxious patients exhibit moist and cool feet. Increased sole temperature can be a sign of diabetic neuropathy.2 A typical sole temperature is about 75°F while this patient’s sole measured 95°F. Plantar psoriasis may present with significant vasodilation and palpable heat along with the typical erythematous plaques.

   As far as the dermoscopy examination goes, Lallas and colleagues studied 83 patients with psoriasis and 86 patients with dermatitis, lichen planus or pityriasis rubra.3 The authors found dotted vessels in a regular arrangement over a light red background and white scales to be highly predictive of psoriasis. Dermatitis patients more commonly showed yellow scales and dotted vessels in a patchy arrangement. Pityriasis rubra was characterized by a yellowish background, dotted vessels and peripheral scales while whitish lines (Wickham striae) were visible exclusively in patients with lichen planus.4

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dinovisjpsays: December 11, 2013 at 11:33 am

One diagnosis I would add to the differential in light of the patient's contact with two family members at risk is Norwegian crusting scabies. Scabies does not spare the dorsal or volar surfaces however.

The ectoparasite can be ruled out by its absence in scrapings of the exfoliated thickened epidermis by a dermatopathologist. I will be checking out the book for purchase at the New York Conference. Thank you Drs. Bodman, Vlahovic and Schleicher.

Jim DiNovis, DPM

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