The main systemic causes of itching are:
- Pregnancy-related problems
- Lymphoproliferative (especially systemic mastocytosis) and hematopoietic disorders, including iron deficiency anemia
- Endocrinal problems such as hypothyroidism and diabetes mellitus
- Drug side effects, such as opioids and drugs which cause cholestasis.
- Allergic reactions
Therefore, in the absence of primary skin findings, a basic workup for itching might include:
- CBC with differential, peripheral blood smear, iron, total iron-binding capacity, serumferritin
- If polycythemia is found, order erythropoietin level and PCR for JAK2 mutation
- Liver chemistry studies
- Serum electrolytes and glucose
- Pregnancy testing
Symptomatic treatment is with antihistamines, topical or oral glucocorticoids, antipruritic lotions and emollients. (Habif, p. 595). “Intense unremitting itching unresponsive to prednisone suggests scabies or dermatitis herpetiformis,” (id at 368), so, in appropriate settings, ask these patients about gastrointestinal symptoms and about close contacts with similar symptoms.