Itchy Skin

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.

Only takes a few of these guys to set off some serious itching

Dermatologic

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.

Systemic Disease

  • 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.

Brachioradial pruritus

Neurologic

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 

  • 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.

If you are itching after reading this post, that is probably psychogenic itching. Good luck!

Pick a card, any card

This post is inspired by a clinic conversation yesterday. Our clinical question was about which antidepressant to choose.  It can kind of feel like a game at times: you make a random pick,and see what happens. Is there a more evidence based way to go about it?  

The evidence behind SSRIs is a whole different post, but suffice it to say that they have similar efficacy and tolerablity. Citalopram (Celexa), Paroxetine (Paxil), Fluvoxamine (Fluvox), Fluoxetine (Prozac), Sertraline (Zoloft), and Escitalopram (Lexapro) are all available widely.

So how to decide what to prescribe when a patient is sitting in front of you. You could pick based on your favorite commercial, or which drug rep bought the best dinner, but maybe there is a less biased method.

Generally we use patient preference, side effects, and cost as the driving factor in picking among similar medicines.  So I thought I’d review the last two for you here.

Cost is easier.  All of these come in generic forms now.  Citalopram and paroxetine are on the $4 drug list at WalMart. A quick search on GoodRx shows prices around $5 for fluoxetine, $8-10 for sertraline, and $15 for fluvoxamine and escitalopram.

Artwork by Robin D Snyder. Text at the bottom of the screen says: “Certain Side Effects May Occur”.

Now for side effects. All of them can cause weight gain, decreased libido, and diarrhea, which are often pretty important to patients. Scarier side effects are QTc prolongation, and hypotension and anticholinergic effects, which may make you think twice about prescribing to an older patient. You can sort out which side effect is most important to your patient, and then steer clear of the worst offenders.

  • Weight gain: Paroxetine seems to be the worst, anecdotally I have had complaints about citalopram as well.
  • Sexual Dysfunction: A big problem with all of them.  Again, paroxetine is the worst, but none are really great.  Your best bet if this is a big factor for your patient: use bupropion instead of an SSRI.
  • GI side effects: Diarrhea is the most common complaint from a GI standpoint.  Sertraline is the worst offender here.
  • QTc prolongation: Citalopram, Escitalopram, and Fluoxetine are the ones known to cause some QT troubles. The others are probably OK.
  • Hypotension and anticholinergic effects: Again, paroxetine is the troublemaker here, although any can contribute.

Often listed as a side effect is agitation or “activation”. Sometimes I try to use this as a benefit.  If patients are particularly apathetic, or have the psychomotor retardation often seen in major depression, you can use this to your advantage.  I think of fluoxetine and sertraline as being more “activating“, while citalopram and paroxetine are more sedating.  The latter two can be helpful for the anxious patient.

At the end of the day, I don’t know that there is a ton of difference between these. I rely on patient experience and preference to guide my choice more than anything else.