Pruritus of Unknown Origin

Focal or widespread linear excoriations, crusts, lichenified plaques, or wheals may be present. Postinflammatory hypo- or hyperpigmentation may also be evident (Figs. 24.1 and 24.2).
Pruritus with no apparent lesions is quite common.
May have secondary infection of lesions (impetiginization).
Possible insomnia and/or depression.
Lesions may have bizarre appearances; therefore, facticia or “neurotic excoriations” should be suspected (see below).

A search for the cause of the pruritus is based on the following:
- A careful history
- Physical findings (linear excoriations, crusts)
The workup for PUO includes the following:
- Rectal and pelvic examinations, if indicated
- Complete blood count
- Stool examination for parasites and occult blood
- Chest radiograph
- Thyroid, renal, and liver function tests
- Follow-up of the patient for as long as necessary to make a diagnosis

Management

Whenever possible, treatment of the underlying systemic disease that is causing the pruritus may bring relief.
Antihistamines are of more benefit in the treatment of allergic conditions, urticaria, and drug reactions than they are for the treatment of itching and may be no more effective than a placebo. Despite this finding, the powerful effect of antihistamines as placebos and as soporifics should not be overlooked.
Topical therapy that can be soothing and helpful in some patients includes the following:
- Menthol, phenol, camphor, and calamine lotions (e.g., Sarna, Prax, PrameGel).
- Cold applications of frozen vegetable packets may be helpful.
- Topical steroids are generally not very helpful when no lesions are apparent.
Gabapentin (Neurontin) and a serotonin re-uptake inhibitor such as sertraline hydrochloride (Zoloft) may be successful in relieving intractable pruritus.

Helpful Hints

The dosage of antihistamines should be titrated gradually upward using nonsedating agents during the daytime and sedating agents at bedtime.
It is important not to overlook a drug reaction as the cause of PUO.
Scabies should be considered if more than one family member itches.
Hodgkin disease may present with PUO that precedes the diagnosis by up to 5 years.
Topical emollients are an essential component of the therapy of pruritus when xerosis is present.

Point to Remember