Deciphering challenging eczema requires thinking outside and inside the box

In considering alternate diagnoses, Sheila Friedlander, M.D., says she considers etiologies that are outside, inside, and “outside, then inside” the box.

“When you see an eczematous eruption, be sure to rule out scabies. Also, if the baby is sick, consider that the eczematous eruption may be a manifestation of zinc or other metabolic deficiency, and realize that children with an allergic contact dermatitis can develop a systematized reaction if they are exposed to the antigen systemically,” says Dr. Friedlander, professor of clinical pediatrics and medicine, University of California, San Diego.

Scabies itch

When taking a history for a child with eczema, initial questions typically include age of onset and family history of eczema. Then, if the rash is recalcitrant to therapy, consideration whether medications are being used correctly.

Dr. Friedlander says that during the course of her 20-year career, however, she’s seen that scabies can be common among children referred for difficult eczema, and she has learned to ask whether any other family members are itching; examines the family members if they are present; and does a scraping for diagnosis if scabies is suspected. If the findings from the microscopic exam are positive, it is worthwhile letting the family members see the bug.

“I usually prescribe topical permethrin 5 percent, but compliance, especially with the head-to-toe treatment required, can be a problem. The sight of the swimming bug under the microscope seems to be an effective motivator for getting the family to use the medication.” she says.

Zinc deficiency

Atypical distribution of the eczematous eruption, especially in an acral area, provides an initial clue to zinc deficiency. Look around the mouth, in the genital area and at the hands and feet, Dr. Friedlander says. For children with this presentation, the next issue to consider is whether the child shows other signs of zinc deficiency, including poor growth, vomiting or diarrhea. Look for hair loss, stomatitis and glossitis, she says.

Zinc deficiency can be evaluated by using a measurement of serum alkaline phosphatase, which is a zinc dependent enzyme that will be low if zinc is low, Dr. Friedlander says. When evaluating the patient’s serum zinc level, blood must be collected in plastic or acid-washed tubes since regular glass tubes may be contaminated with zinc.

Zinc deficiency can be due to an inherited autosomal recessive disorder in which the patient lacks the intestinal zinc transporter. These children may be fine while breastfeeding, and then manifest with the signs of zinc deficiency once they are off their mother’s milk. Another cause in breastfeeding children is low zinc in the mother’s milk because of defective secretion of zinc into the milk, and a third cause is malabsorption due to lack of pancreatic enzymes, she says.

“If a child has zinc deficiency and evidence of malabsorption (diarrhea, failure to thrive), consider cystic fibrosis and refer patients for diagnostic evaluation,” she says, adding that “zinc deficiency masqueraders” should be considered if the zinc level is normal.

Outside going in

Systematized contact dermatitis should be considered for a child with an allergic contact dermatitis who presents with an eruption that cannot be explained by topical exposure to the allergen, Dr. Friedlander says. In a case she presented, a teenager who had been diagnosed with nickel allergy after presenting with a rash around her navel had improved after avoiding belts and pants with metal closures. Subsequently, she presented with a rash involving her entire body, with the most severe rash on her legs.

Dr. Friedlander says the rash on this patient’s legs was from exposure to nickel - she was shaving her legs with a nickel-containing razor blade. The patient’s symptoms cleared after discontinuation of shaving, but relapsed subsequently. Ingesting foods containing low concentrations of nickel is a common route of systemic exposure, and institution of a nickel-free diet in the patient led to prolonged remission.

“Systemic contact dermatitis is a systemically reactivated allergic contact dermatitis that can occur when an exquisitely sensitized person develops a reaction after systemic exposure to the substance that usually causes allergic contact dermatitis,” Dr. Friedlander says.

She suggests collaborating with a contact dermatology expert who can provide dietary recommendations.

“Although zinc deficiency and systematized contact dermatitis are uncommon, keep them in mind for your little or big patients with refractory eczematous disorders,” she says. DT

Disclosures: Dr. Friedlander reports no relevant financial interests.