Inspired by last Friday’s AMR case, I thought I’d write an overview of the causes of pruritus, particularly the causes that DON”T go along with a rash (because I hate rashes? Nah). You can organize these causes in a few ways, but I like to think of them based on the big categories of: dermatologic, systemic disease, neurologic, and psychogenic.
Most dermatologic etiologies are going to have an associated rash, but it may be subtle. Here are a few where you make have to look closely:
- Xerosis: The most common cause of generalized pruritus, just plain old dry skin. Common in winter, often can tell skin is try just by feeling it.
- Scabies: Regular scabies, not the Norwegian kind discussed in AMR, may not have much of a rash associated. Sometimes you can see a burrow, but rarely. I learned that the itching is a delayed hypersensitivity reaction, and may not appear for weeks after infestation.
- Atopic Dermatitis: Think of this in a patient with other allergic phenomena (rhinitis, conjunctivitis), sx at an early age, and a family history of allergic disease. Patients also have allokinesis, when an innocuous stimuli, like temperature changes or clothing, induces itching.
- Contact dermatitis: there are two kinds of contact dermatitis. Irritant contact dermatitis (like that caused by poison ivy) occurs when an irritant directly damages the skin. There is often a rash in this instant. Allergic contact dermatitis occurs when the irritant induces an allergic response. The rash here may be diffuse and obvious, or may be more subtle. Ask about anything that comes in contact with skin, including soaps, lotions, and laundry detergent.
- Cholestasis: The first thing we think of, but pretty rare. Most commonly starts in the palms and soles before becoming more generalized. Disorders that cause cholestasis include: Primary biliary cirrhosis, cholestasis of pregnancy, viral hepatitis, and anything that causes obstructive jaundice.
- Renal disease: We think about this in uremia, but it is actually common even in dialyzed patients. Worse at night or after a dialysis session,
- Malignancy/hematologic disorders: More often with hematologic malignancies than with solid tumors. Think of: Hodgkin’s disease, Polycythemia vera (worse in water), Carcinoid (thank you, histamine), and cutaneous T cell lymphoma. Patients without a diagnosis for their pruritus may be at increased risk for malignancy.
- Thyrotoxicosis: cause you can’t have a list without thyroid on it. Actually, a fairly common sx of Graves disease. hypothyroidism can cause xerosis, which itches
- Connective Tissue Disease: Common with dermatomyositis and scleroderma in particular.
Small fiber neuropathy may be associated with pruritus, so anything that causes neuropathy could lead to itching, including diabetes. These are typically localized to the affected area, however.
- Post herpetic neuralgia: Up to 50% of patients with post herpetic neuralgia experience this as itching rather than pain.
- Notalgia Paresthetica: Itching on the upper back, perhaps due to trapped nerve fibers in the T2-T6 nerve roots. Unilateral, near the medial or upper border of the scapula.
- Brachioradial pruritis: Itching of the proximal dorsolateral forearm, but may extend up to the upper arm or even trunk. Feels better with ice application. Similar to notalgia paresthetica, this may be related to nerve root entrapment in C5-C8, but also may have something to do with sun exposure.
- MS: Compared to the rest on this list, MS is more likely to cause generalized pruritus. Typically a relapsing, remitting type course that mirrors the rest of the disease.
- Psychogenic excoriation: Skin is normal, but affected individuals pick and scratch at it. Lesions are all within reach of the patient, and may be precipitated by psychologic stressors.
- Delusional parasitosis: Patients experience a firm, fixed belief that they are infested by parasites, despite a lack of evidence of infestation. This may be secondary to another psychiatric disorder, or may be the primary disorder itself.
- No matter the underlying etiology, pruritus may get worse under emotional stress.
For many, the itching itself causes emotional stress. It impacts sleep, work, relationships. Relief can really improve your patient’s quality of life, plus you may uncover a systemic disease earlier.