When A Patient Presents With A Pruritic Lower Extremity Rash

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Author(s): 
William Fishco, DPM, FACFAS

A 50-year-old female presented to the office with the chief complaint of an itching rash on her ankles and feet. She reported the itch to be severe at times. The duration of symptoms was for at least a few months.

   The patient had no prior treatment for the condition. She denied any known cause for it. She denied any new medications, activities, recent traveling or new detergents for laundering her clothes. I asked her if she any rashes elsewhere on her body and she did have a similar rash on the flexor surface of her wrists.

   Her past medical history was remarkable for asthma, diabetes mellitus, gastroesophageal reflux disease and dyslipidemia. Her current medications included insulin, glipizide (Glucotrol, Pfizer) and simvastatin.

   In terms of the patient’s social history, she is married, a non-smoker and only has a mild history of alcohol use. She currently works for the United States Postal Service as a teller in a local branch.

   In regard to the physical examination, her vascular status was remarkable for palpable pedal pulses with brisk capillary refill to the toes. She had normal deep tendon reflexes and no loss of epicritic sensation after testing with a Semmes-Weinstein 5.07 g monofilament. The orthopedic exam revealed symmetric, pain-free range of motion of the ankle, subtalar and midtarsal joints. The dermatologic exam revealed a rash on her ankles and feet. The rash is a cluster of purple-colored plaques with fine scales in a symmetrical fashion on her ankles and wrists.

Key Questions To Consider

1. What is the most likely diagnosis?
2. What is the differential diagnosis?
3. What are the key characteristics of this condition?
4. What is the treatment?

Answering The Key Diagnostic Questions

1. The most likely diagnosis is lichen planus.
2. The differential diagnoses include psoriasis, pityriasis rosea, pityriasis rubra pilaris, granuloma annulare and discoid lupus.
3. The key characteristics include a violaceous plaque and a planar (flat topped) appearance with a fine scale. The scale has a characteristic appearance of gray to white streaks known as Wickham’s striae.
4. Treatment is generally with high potency topical steroids such as clobetasol.

Pertinent Insights On The Differential Diagnosis

The differential diagnosis of well-demarcated scaling plaques and papules without crusting, erosions or fissures includes psoriasis, pityriasis rosea, pityriasis rubra pilaris, lichen planus, granuloma annulare and discoid lupus.

   Psoriasis is an autoimmune disorder of the skin. Plaque psoriasis is a main differential in this case. Plaque psoriasis is characterized by a silvery scale on an erythematous plaque. Itching can be severe with psoriasis. The most common areas of the body in which psoriasis occurs include the scalp, elbows, knees and back. There can be excoriations and crusting of the primary lesion.

   Pityriasis rosea most commonly occurs in young adults and children. The primary lesion is a rose- to fawn-colored plaque in oval shape. The location of pityriasis rosea is usually the trunk. In the classic presentation of pityriasis rosea, a primary lesion will occur followed by satellite lesions one to two weeks later. This is called a herald patch.

   Pityriasis rubra pilaris is a rare condition affecting the palms and soles. It occurs in children and adults. There is yellowing hyperkeratotic skin with red to orange colored scaling plaques.

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