Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.
A 72-year-old man is evaluated for a 3- to 4-month history of diffuse, intractable itching involving most of the body. He uses emollients regularly. He cannot identify any precipitating causes. He was relatively healthy before the onset of the itch but now feels chronically fatigued. The itch is relentless. He has used topical hydrocortisone and oral diphenhydramine without relief from the itching. Medical history is pertinent only for a 25 pack-year history of smoking, and his only medication is aspirin.
On physical examination, his skin is generally well hydrated. Scattered punctate and linear excoriations are present on the upper shoulders, arms, upper back, thighs, and legs. The skin on the midback between the scapulae is normal. No primary skin lesions or icterus is seen.
Which of the following is the most appropriate next step in management?
A: Complete blood count, comprehensive metabolic profile, and thyroid function studies
B: Epicutaneous patch testing
C: Prednisone
D: Skin biopsy
MKSAP Answer and Critique
The correct answer is A: Complete blood count, comprehensive metabolic profile, and thyroid function studies.
Serologic tests to evaluate common causes of itch are appropriate, including a complete blood count, serum chemistries, iron studies, and thyroid studies. A serum protein electrophoresis can be considered. This patient has an itch that is not explained by a rash, and this is a concern for an underlying systemic or neurogenic cause. Important causes of systemic itching include malignancy (particularly lymphoma), cholestatic liver disease, chronic kidney disease, thyroid disease, iron deficiency, certain medications (opiates), and HIV infection. Patients with this type of itch have no primary skin findings but can develop excoriations and even an eczematous dermatitis from repeated scratching. Evaluation for an underlying cause of itch is appropriate whenever the degree of itch seems to exceed the identifiable dermatitis. In patients with pulmonary symptoms or at risk for lung cancer, a chest radiograph may help evaluate for an occult malignancy. Other imaging studies should be considered based on history and findings on physical examination. Patients with this type of itch should undergo age- and sex-appropriate cancer screening, if they are not up-to-date.
Epicutaneous patch testing is the diagnostic gold standard for allergic contact dermatitis; however, this diagnosis should not be considered in the absence of an eczematous dermatitis. Treatment with systemic corticosteroids could mask symptoms and result in an inappropriate or delayed diagnosis. A skin biopsy is unlikely to help establish a diagnosis in the absence of any relevant skin findings.
Key Point
- Diffuse itching in the absence of a rash requires a thorough evaluation of an underlying systemic cause.
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