A 92-year-old female presented to my office with a chief complaint of an itching rash on her legs and feet. She has had symptoms on and off for decades and related that the rash “flares up” from time to time. The patient used various creams prescribed by her primary care physician and dermatologist over the years. Recently, she moved to my area to be close to her family. She ran out of medication and needed help.
Her past medical history was remarkable for hypertension, hypercholesterolemia, hyperuricemia and osteoporosis. Her current medications included allopurinol, amlodipine, Vitamin D3, valsartan with hydrochlorothiazide, magnesium oxide, simvastatin, and tramadol. She denied any past surgeries. The patient ambulated without assistance.
The physical exam revealed a well-dressed and well-nourished female. Her vascular exam revealed weakly palpable pulses bilaterally with a brisk capillary refill. In regard to the neurologic exam, there were no deficits with symmetric deep tendon reflexes and light touch sensation intact. The dermatologic exam revealed numerous areas of rash on both of her feet and legs. The rash included isolated, well-defined maculopapular lesions with scale (see photo above). In general, the skin was thin and atrophic. The patient’s toenails were healthy without any obvious dystrophy or fungal infection. When it came to the orthopedic exam, the patient had pain-free and full range of motion of the ankle, subtalar, and midtarsal joints bilaterally.
Key Questions To Consider
1. What is included in the differential diagnosis?
2. What is the most likely diagnosis of this patient’s rash?
3. What are the key characteristics of this condition?
4. What are the treatment recommendations for this condition?
Answering The Key Diagnostic Questions
1. Tinea pedis, eczema, psoriasis, lichen planus and contact dermatitis.
3. Well-demarcated erythematous plaques with silvery scales.
4. First-line treatment is a high-potency topical steroid. In difficult cases or when topical steroids have failed, referral to a dermatologist is recommended. Other treatment options may include UV light treatment, oral cyclosporine, methotrexate, acitretin or biologic therapies.
Working Through The Differential Diagnosis
The differential diagnosis for the aforementioned patient includes tinea pedis, eczema, psoriasis, lichen planus and contact dermatitis.
Tinea pedis is one of the most common rashes on the foot. Typical presentations include the acute variety, which is typically wet with vesicles and blisters in the web spaces. Fissuring of skin in the web spaces is common, especially when macerated, and typically involves the third and fourth interdigital spaces. The chronic type of tinea pedis is generally dry with scales, fissures and lichenification in a moccasin distribution. Although tinea pedis can occur on the dorsal aspect of the foot, the most common areas affected are the toes and the plantar foot. Tinea pedis is less likely than contact dermatitis to be symmetrical. Often, chronic tinea pedis is especially problematic when there is a concomitant onychomycosis infection, which acts as a reservoir for dermatophytes.
Eczema is an inflammatory skin condition, which likely has environmental and genetic components. Eczema often affects patients with food sensitivities, asthma and hay fever. In my practice, atopic eczema is more typical in infants and children. There is usually a family history of atopy. Most of the time, the condition resolves in adulthood.
Dyshidrotic eczema exhibits tiny vesicles that develop on the sides of the toes and fingers, and leads to scaling and desquamation of skin. Nummular (discoid) eczema is characterized by larger coin-shaped rashes with scale (see photo above). It is not uncommon to see vesicles and lichenification of skin due to scratching.
Lichen planus is a rash that clinicians can remember by the five “Ps”: purple, planar, peripheral, pruritic and polygonal (see photo above). The current thinking is that lichen planus is a cell-mediated autoimmune disorder against keratinocytes. When certain drugs induce lichen planus, this is a lichenoid drug eruption. The most common drugs associated with a lichenoid eruption include beta-blockers, NSAIDs, ACE inhibitors, gold, sulfonylureas, penicillamine, anti-malarial drugs and thiazides. Systemic conditions that may cause lichen planus include diseases of the liver such as hepatitis and cirrhosis.
Contact dermatitis is caused by an allergic reaction to the skin (see photo above). Irritant contact dermatitis is usually caused by chemicals such as industrial solvents, latex and soaps. Allergic contact dermatitis can be caused by sensitivity to metal (nickel and gold) and plant material, such as poison ivy. Shoe contact dermatitis can be caused by hypersensitivities to glue, rubber, dyes or tannins. Keep in mind that shoe contact dermatitis can lead to a symmetrical pattern of rash on the feet.
The correct diagnosis for the patient in question is psoriasis, a chronic non-infectious inflammatory dermatosis characterized by well-demarcated erythematous plaques with silvery scales. There are a number of types of psoriasis that include plaque (most common), guttate, inverse, pustular and erythrodermic. Plaque psoriasis has patches of circle- to oval-shaped red plaques. This is the most common psoriasis presentation that one will encounter in a podiatry practice.
Keys To Differentiating Psoriasis From Eczema
It may be difficult to distinguish plaque psoriasis from eczema as many of their signs and symptoms overlap. However, there are some features that are unique to each.
• Psoriasis causes well-defined, erythematous patches with a silvery colored scale. Thick patches of erythema without scale are common too. The most commonly affected areas include the scalp, elbows and knees. Always ask the patient if there are rashes anywhere else on the body or a history of rash in the aforementioned areas.
• Eczema tends to appear between the toes and fingers as well as the flexural creases of the arms and legs.
• Eczema has a red to brown-gray coloration. One often sees weeping and crusting with eczema, and these characteristics are not typical features of psoriasis.
• Always remember to ask about the presence and intensity of itching. Psoriasis, as a general rule, causes mild itching whereas eczema-associated itch is more severe. Also, with eczema, itching seems to be worse at night. Infants and children rarely have psoriasis.
• Psoriasis usually develops somewhere between 15 and 35 years of age. On the contrary, clinicians typically see eczema in younger patients, usually those in infancy through young adulthood.
• Psoriasis is also associated with a Koebner phenomenon, which is related to developing additional lesions in areas of skin trauma or irritation.
Current Treatment Options For Psoriasis
Treatment of psoriasis generally begins with a prescription of a super high potency topical steroid ointment, such as clobetasol. In difficult to treat cases or when topical steroid therapy has failed, a dermatology referral may be appropriate. Other available treatments include UV light treatment, oral cyclosporine, methotrexate and acitretin.
One may also consider biologic therapies including adalimumab (Humira®, AbbVie), brodalumab (Siliq™, Ortho Dermatologics), certolizumab pegol (Cimzia®, UCB), etanercept (Enbrel®, Amgen®), guselkumab (Tremfya®, Janssen Biotech), infliximab (Remicade®, Janssen Biotech), ixekizumab (Taltz®, Lilly), secukinumab (Cosentyx®, Novartis Pharmaceuticals) and ustekinumab (Stelara®, Janssen Biotech).
In summary, a patient presented with a rash on both lower extremities and it was psoriasis. Often in practice, it can be challenging to differentiate three common scaling rashes: tinea pedis, eczema and psoriasis. Remember to think about age, location (not just the lower extremities) and intensity of itch. Finally and probably most importantly, one should ask the patient, “Have you ever been diagnosed with psoriasis or eczema?” “As a child, did you have problems with rashes, hay fever or asthma?” These lines of questioning can help you make the most accurate diagnosis. A skin biopsy may also be indicated if the diagnosis is still unclear. When considering tinea pedis versus eczema, a skin scraping (PAS stain) can rule out a dermatophyte infection.
Generally speaking, clinicians often make the diagnosis of challenging dermatological conditions after a careful history and physical exam focusing on identification of key characteristics of the skin lesion.
Dr. Fishco is board-certified in foot surgery and reconstructive rearfoot and ankle surgery by the American Board of Podiatric Surgery. He is a Fellow of the American College of Foot and Ankle Surgery, and a faculty member of the Podiatry Institute. Dr. Fishco is in private practice in Phoenix.