Treating A Patient With Pruritic, ‘Swollen’ Legs
Some detective work may be involved to determine what instruments of perpetuation the patient is using. Many patients believe it is appropriate and necessary to scrape away almost any degree of normal callus formation from their heels as the beauty magazines recommend. This can lead to lichenification and spread of the lesions into thick hyperpigmented plaques.
Neurodermatitis presents as one stage in a spectrum of scratching or rubbing disorders in our patients. First, a solitary, localized coin-shaped plaque of nummular eczema develops. A single finger rubbing one reachable spot may initiate the condition. Repetitive rubbing can establish the itch-scratch cycle, which may progress to larger, thicker plaques of fissured lichenification within weeks. Some lesions may become excoriated. Secondary infection can develop. Months of continual itching and scratching produce thick plaques of lichen simplex chronicus and later nodules of prurigo nodularis. We can consider all of these manifestations of neurodermatitis as localized cutaneous zones of depleted cortisol, perpetuated by centralized reflex.
It is interesting to note that histologically, chronic neurodermatitis or lichen simplex chronicus are quite similar to pressure keratoses. Common features include hyperkeratosis, acanthosis and parakeratosis pointing to similar mechanisms of repetitive rubbing and friction. Shoes or a supporting surface that repetitively rubs skin over a prominent joint can produce localized hyperkeratotic plaques of lichen simplex chronicus.
A Guide To The Differential Diagnosis
Pujol and colleagues have listed 33 local and 38 systemic causes of persistent pruritus.3 Alarmingly, an invisible form of mycosis fungoides can present as pruritus without any rash and only a biopsy can diagnose it.4 Patients with persistent pruritus deserve a dermatology consult.
A laundry list of differential diagnoses can be confusing and slow down our clinical thinking. Nousari suggests simply limiting our list of differentials to the following four thought paths.5
1. Primary impression. At the top of your list should be what your gut tells you. This works well as long as it is a disease you have seen or heard of before.
2. Mimicker. What would be the chief mimicker of the primary impression? In this case, it should be a member of the papulosquamous family of disorders. Considering similar presentations, psoriasis is an appropriate mimicker. One can easily miss psoriasis when it presents solely on the foot without accompanying telltale extensor surface lesions. Inspecting the scalp, knees and elbows for scaly plaques is often helpful to confirm a clinical impression of pedal psoriasis.
3. Worst case scenario. What diagnosis, if missed, would cause the most harm to the patient? The group of cutaneous T-cell lymphomas may present with persistent pruritus and erythrodermic plaques. Biopsies and consultations are important in chronic lesions that do not improve with topical therapies.
4. Esoterica. In order to satisfy our intellectual need to consider the most remote of diagnostic possibilities, our differential diagnosis list would not be complete without a rare bird. Dermatitis herpetiformis rarely presents on the foot but it is appropriate to consider it in this case because of its characteristic symptoms of intense pruritus and excoriations. Dermatitis herpetiformis is an autoimmune blistering disorder associated with gluten-sensitive enteropathy. It classically affects the extensor elbows, knees, buttocks and back.6 One can diagnose this via cutaneous biopsy and direct immunofluorescence showing deposition of immunoglobulin A in a granular pattern in the upper papillary dermis. Treatment is based on a gluten-free diet and dapsone (Aczone, Allergan).6