Scratching, but no rash.
The physician is often faced with the patient whose chief complaint is itching. What follows is a brief summary of the approach to such a patient.
Does the patient have a rash easily seen from 3 feet away? If no, put on gloves (just in case the patient has scabies). Look for the typical burrows of scabies in the web spaces and wrists. If other family members itch, the possibility of scabies is increased (but may also occur in say insect bites). Examine the entire skin. Look for dry skin which is the most common cause of diffuse itching in the elderly. If this is suspected, a trial of an emollient cream or vaseline after the shower daily may be in order. Often, eczema accompanies dry skin and appears as red, rough, scaly areas. A potent topical steroid may be helpful here.
Is there any primary lesion, e.g., pustule, vesicle, papule, etc.? Pustules may represent a bacterial infection, vesicles an allergy or dermatitis herpetiformis and papules or blisters may result from insect bites.
Take a tongue blade and rub lines on the patient's back to see if dermatographism is present. If so, a 3 day trial of antihistamines is in order.
Make sure you know all the drugs (and supplements) the patient is on and if any can cause pruritus. What medical problems does the patient have? Liver or kidney dysfunction, Hodgkin's lymphoma, and thyroid disease can all cause itching. Diabetes alone does not cause itching but it does predispose to xerosis which does itch. Is there any recent weight loss? Lymphadenopathy? These two could signal an underlying malignancy. Ask the patient why s/he thinks s/he is itching. Sometimes you will get, "You're the doctor," but other times you will get a clue to the problem, e.g., "At times I have seen something move!," which may signal delusions of parasitosis or true infestation by pediculosis pubis. Finally, make sure the patient truly itches and isn't just scratching out of habit or because of stress.
Dry Skin. Dry skin itches! Worse in the winter, with frequent water contact and in atopics (Is there allergy, hay fever, eczema in patient or family members?).
Scabies. If there is any suspicion of scabies, put on gloves and examine the hands and feet. Here, a classic scabies burrow is shown on the side of the foot.
Dermatographism. Rub the back with a tongue blade (and wait 2 minutes) to create the linear wheals of dermatographism.
Small Fiber Neuropathies
Diffuse itch in the Elderly: One study of diffuse itch in the elderly found lower sebum content and higher transepidermal water loss [JEADV 2016;30;549]. The authors suggested the use of moisturizers with higher lipid content (grease).
Neuropathic Pruritus. Neuropathic pruritus is itch not from a primary skin disease, but instead a neurologic one. Examples include brachioradial pruritus (some forms), notalgia paresthetica, meralgia paresthetica, multilevel symmetric neuropathic pruritus, and scalp dysesthesia.
Delusions of Parasitosis
CNS-Related, e.g, post-stroke
Invisible Cutaneous T Cell Lymphoma. Rarely, an elderly patient with diffuse itching but normal skin will show cutaneous T cell lymphoma on biopsy [JAAD 2000;42;324]. Thus, a random skin biopsy in a patient with unexplained itch is not unreasonable. As a side note, a random skin biopsy is not unreasonable in a patient with chronic fever of unknown origin. Intravascular lymphoma may be found [J Cutan Pathol. 2017;44(9):729-733.].
Bile duct Malignancy
Hyperferritinemia (iron overload) [Dermatology Online Journal 21(9)]
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