Scabies vs. Psoriasis: Identifying the Differences in Symptoms

February 7, 2024

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Psoriasis and scabies are two distinct skin conditions that can initially present similar symptoms like redness, scaling, and itching. However, understanding the key differences between psoriasis and scabies is crucial for prompt diagnosis and effective treatment.

Overview of Psoriasis and Scabies

Psoriasis is a common, chronic, autoimmune condition characterized by areas of inflamed skin covered with silvery-white scales known as plaques. The most common form is plaque psoriasis, accounting for 80-90% of cases. Other types include guttate psoriasisinverse psoriasis, and erythrodermic psoriasis. Psoriasis flare-ups can range from mild with small areas of involvement to widespread inflammation with severe scaling. Flare triggers include stress, skin injuries, certain medications, and infections.

Scabies, on the other hand, is a contagious parasitic skin infestation caused by the human itch mite Sarcoptes scabiei var. hominis. An infested person develops an intensely itchy scabies rash due to a delayed hypersensitivity reaction to the mites, eggs, and feces. Common sites include the webs of fingers, wrists, elbows, axillae, penis, nipples, and waist. Scabies spreads rapidly under crowded conditions by prolonged skin-to-skin contact with an infested person. Crusted scabies is a severe variant seen in immunocompromised patients.

Key Differences

ParameterPsoriasisScabies
Type of diseaseChronic autoimmune conditionContagious parasitic skin infestation
CauseFaulty immune system triggers inflammation and rapid skin cell growthSarcoptes scabiei mites burrow into skin
Areas affectedExtensor surfaces like elbows and knees as well as the scalpWebs of fingers, wrists, elbows and genital area
Primary symptomsThick red patches with silver-white scalesExtremely itchy rash and tiny burrows on skin
Time of itchingConstant, but worsens at nightWorse at night
SpreadNot contagiousHighly contagious with skin contact
DiagnosisClinical exam, skin biopsySkin scraping to detect mites/eggs under microscope
TreatmentTopical creams, phototherapy, oral medications, biologicsTopical scabicides, oral ivermectin
CourseChronic relapsing, requires long-term managementCurable with 1-2 treatments, if regimen completed

As evident from the table, there are marked dissimilarities between psoriasis and scabies in terms of pathogenesis, areas affected, symptoms, diagnosis and treatment approach. Let’s examine some of these key points in more detail.

Clinical Manifestation and Symptoms

The most common psoriasis symptoms include:

  • Sharply demarcated red plaques with a covering of characteristic silver-white scales
  • Plaques usually seen over extensor surfaces like knees, elbows and scalp
  • Itching, pain or bleeding if plaques crack open
  • Pitting and discoloration of nails
  • Joint swelling, pain and stiffness in psoriatic arthritis cases

Scabies symptoms, on the other hand, include:

  • Intensely itchy skin rash composed of tiny bumps and blisters
  • Thin, S-shaped burrows visible on skin
  • Rash occurring around finger webs, wrists, elbow creases, breasts, groin area
  • Severe nighttime itching
  • Sores and crusty skin due to excessive scratching

So while both conditions may have red, inflamed areas with itching, psoriasis has distinct silver scaling while scabies manifests with noticeable burrows and rashes confined to specific body zones.

Etiology and Pathogenesis

Psoriasis Pathogenesis

Psoriasis occurs due to a faulty immune response wherein inflammatory T-cells mistakenly attack healthy skin cells. Activated cytokines like tumor necrosis factor-α stimulate keratinocytes and dermal blood vessels, accelerating skin cell turnover. As a result, immature skin cells build up rapidly on the skin’s surface causing red, scaly plaques.

Genetic susceptibility along with environmental triggers like infections, stress, medications and skin trauma initiate psoriasis flares. Once triggered, it follows a chronic relapsing course.

Scabies Etiology

Scabies is caused by the parasitic mite Sarcoptes scabiei variety hominis. The adult female mite burrows into the epidermis and deposits eggs and feces as it moves, which incites an intense allergic reaction.

Skin-to-skin transfer from an infected individual aids the spread of this highly contagious condition. Overcrowded living conditions further propagate scabies outbreaks. In crusted scabies, the mite population is uncontrolled leading to thick crusty skin.

Diagnosis

Distinct diagnostic tests confirm psoriasis and scabies respectively. These include:

Psoriasis diagnosis

  • Clinical skin examination – silvery scales on red plaques are classic
  • Skin biopsy – to rule out other conditions
  • Nail examination for changes like pitting, crumbling and discoloration

Scabies diagnosis

  • Skin scraping – microscopic identification of mites, eggs, or feces
  • Burrow ink test – ink rubbed on skin outlines path of burrows
  • Skin biopsy shows mite parts in case of ambiguity

Treatment Considerations

While both conditions cause irritation and discomfort, treatment considerations differ significantly:

Psoriasis Management

As it is an ongoing autoimmune disorder, most people require lifelong psoriasis management with long-term medications and lifestyle adjustments to control flare-ups.

  1. Topical treatments – corticosteroids, retinoids, calcineurin inhibitors and vitamin D analogues
  2. Phototherapy – exposure to UV light under medical guidance
  3. Oral systemic medications – methotrexate, retinoids
  4. Biologic drugs – adalimumab, infliximab, ustekinumab

Dealing with triggering factors, practicing skin care, avoiding smoking and alcohol, and managing stress levels also help mitigate flare-ups.

Scabies Treatment

Since it is an infectious condition, scabies can be cured using topical scabicides and/or oral medications. Treatment aims to kills mites and eggs and provide symptomatic relief.

  • Topical scabicides like permethrin, lindane, benzyl benzoate or crotamiton
  • Oral ivermectin – especially for crusted scabies
  • Antihistamines and medicated oils to reduce itching
  • Maintain skin hygiene and disinfect surfaces

Treatment is repeated after 1-2 weeks to eliminate any surviving mites and eggs. Close contacts must also undergo prophylactic treatment to prevent reinfestation.

Conclusion/Summary

In summary, psoriasis and scabies may initially appear similar due to associated redness and itching. However, psoriasis results from an autoimmune attack on skin cells causing silver-white plaques. In contrast, scabies is caused by S.scabiei mites burrowing into skin leading to severe itching and rashes. While psoriasis has a chronic course with fluctuating symptoms, scabies is contagious but curable condition with appropriate topical and/or oral treatment. Distinguishing features on examination and diagnostic tests aid in confirming the exact diagnosis. Long term management is needed for psoriasis, whereas scabies can be eliminated with completion of the treatment regimen.

Frequently Asked Questions

What is the main difference between psoriasis plaques and scabies rashes?

Psoriasis causes thick scaly plaques covered with silvery white scales. Scabies leads to an extremely itchy rash composed of tiny red bumps, blisters or scaly skin without silvery scaling. Scabies also forms thin, snake-like burrows visible on the skin surface unlike psoriasis.

Can scabies be mistaken for psoriasis?

Yes, the appearance of scabies rash alone can be confused with psoriasis in the early stages. The distribution patterns also may overlap. However, scabies involves itch mite burrows and is severely itchy, especially at night unlike psoriasis. Appropriate diagnostic tests can accurately differentiate between scabies infection and psoriatic plaques.

No, psoriasis and scabies do not have any direct correlation. Their pathogeneses differ markedly. Psoriasis is caused by faulty immune mechanisms while scabies is due to a human itch mite infestation. Flare-ups in psoriasis does not predispose towards getting scabies. However, severe scabies infection can worsen inflammation in pre-existing psoriasis.

How to prevent scabies and psoriasis flare-ups?

Avoiding known triggers is key to preventing psoriasis flares, which include – skin trauma, respiratory infections, stress, certain medications, alcohol and smoking. For scabies, avoiding direct skin contact with infected persons prevents transmission. Practicing good hygiene, disinfecting bedding/clothes and prompt treatment of infected contacts also prevents scabies spread.

What are the first-line treatment options for scabies and psoriasis?

Topical preparations constitute first-line treatment for both conditions:

  • For scabies – topical permethrin, lindane, benzyl benzoate, crotamiton
  • For psoriasis – topical corticosteroids, retinoids, vitamin D analogues

Based on severity, phototherapy or systemic oral medications may be warranted for psoriasis. Severe crusted scabies requires addition of oral ivermectin along with topical scabicides.

Key Takeaways

  • Psoriasis is an autoimmune condition causing red, thick scaly plaques while scabies is a parasitic skin infestation leading to severely itchy rash and burrows.
  • While both can show redness and irritation, scabies itch intensifies at night unlike psoriasis. Scabies also spreads via direct contact.
  • Psoriasis requires long term treatment and control of flares while scabies can be definitively cured.
  • Distinct diagnostic tests and distribution patterns of lesions help differentiate between these conditions.
  • Understanding the pathogenesis and treatment approach for both aids prompt diagnosis and effective management.

References

  1. Rendon A, Schäkel K. Psoriasis pathogenesis and treatment. Int J Mol Sci. 2019;20(6):1475.
  2. Goldust M, Rezaee E, Raghifar R, Naghavi-Behzad M. Ivermectin vs. lindane in the treatment of scabies. Ann Parasitol. 2013;59(1):37-41.
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