Essential Insights On Treating Psoriatic Lesions In The Lower Extremity

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Author(s): 
M. Joel Morse, DPM

A Guide To Making A Differential Diagnosis

Psoriasis may occasionally resemble atopic dermatitis or eczema. However, it will usually be thicker, redder and more sharply demarcated than eczematous lesions. Psoriasis usually affects the extensor surfaces whereas eczema typically involves the flexor surfaces.15

   Psoriatic plaques may occasionally resemble seborrheic dermatitis, tinea infections, cutaneous T-cell lymphoma, ichthyosis, secondary syphilis and Reiter’s syndrome. Other differential diagnoses include contact dermatitis, stasis dermatitis, nummular dermatitis, candidiasis, drug eruption and mycosis fungoides.

   As podiatric physicians, we may see patients before the internists or pediatrician. Accordingly, we are on the frontlines and often act as the “triage” doctor as we decide what other specialists are needed for the best care for the patient. When it comes to patients with psoriasis, you must look at the whole body for other sites of skin involvement to help key into their diagnosis or diagnoses. Look at the face, neckline, hairline, elbows and knees. Patients with psoriasis have increased cardiovascular risk factors, including hypertension, diabetes mellitus, dyslipidemia, obesity and smoking.6 Those who have childhood obesity are also at risk.

   In the cases in which physical examination and clinical history are not diagnostic, skin biopsy may be indicated to make the diagnosis. I would recommend two 2-mm or 3-mm punches in the center of the “inflamed” area. If the scaling only affects a small area of the foot and does not show up elsewhere on the body, it is advantageous to biopsy.

   We are at a disadvantage in comparison to the dermatologists or internists who have a larger “playing field” and more skin to observe. While one does want to do full body exams, it is not always feasible in terms of time. In my practice, I routinely biopsy any skin that scales and skin for which I do not have a definite diagnosis. I would also make it a point to biopsy on the spot if the patient is in the office for the “skin” problem. If the finding is secondary to another issue of more concern, schedule the biopsy for another visit.

Pertinent Insights On The Classification Of Psoriasis

There are varied clinical presentations of psoriasis. It has been broadly classified into non-pustular and pustular psoriasis. Non-pustular psoriasis is more common and can be organized into plaque, guttate, inverse and erythrodermic psoriasis. The plaque type is more common and occurs in 85 to 90 percent of patients with psoriasis. It is also known as psoriasis vulgaris.16 The lesions are often symmetrical.16 As podiatrists, we see the following phenotypes: the classic plaque type, the palmoplantar type, the interdigital type and nail psoriasis.

   Different studies show different results. Under the “plaque” phenotype, one study observed that the most common sites of involvement in descending order of frequency were trunk, limbs, scalp, face, palms-soles and flexures.17 The second most common clinical phenotype was palmoplantar psoriasis followed by flexural psoriasis.17 Kaur and co-workers reported the scalp (25 percent) as the most common first site of involvement followed by legs (20.6 percent) and arms (11.7 percent).18

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