8 Medical Conditions That Mimic Psoriasis

Why a Differential Diagnosis Remains Essential

Medical consultation
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Psoriasis is challenging to diagnose, in large part because doctors must primarily rely on the appearance of the lesions (plaques), which can look similar to skin changes resulting from other concerns, such as eczema, dermatitis, and even lupus and skin cancer. On top of that, there are different types of psoriasis with variations in their appearance, location, and severity.

Because of this, it is not uncommon to misdiagnose psoriasis or, conversely, to incorrectly diagnose another condition as psoriasis. To avoid this, dermatologists will commonly perform a differential diagnosis to rule in or out diseases and conditions with symptoms similar to psoriasis. By excluding other possible causes—using blood tests, cultures, skin biopsy, and other tools—they can accurately confirm the diagnosis and start the appropriate treatment.

Your psoriasis symptoms very well could be due to psoriasis. But here are eight medical conditions your doctor will likely consider before coming that conclusion.

Eczema

Eczema is the name for a group of conditions that cause red, itchy skin patches similar to psoriasis. As opposed to psoriasis, an autoimmune disorder, eczema is characterized by an overactive (rather than self-destructive) immune response.

Eczema tends to be itchier than psoriasis and can cause oozing and crusting when scratched. With psoriasis, the plaques can easily bleed when scratched, leaving behind a peppered pattern of blood spots known as the Auspitz's sign.

The differences are most apparent under the microscope. With psoriasis, the skin cells will appear acanthotic—dense and compressed due to the accelerated speed of skin growth. With eczema, no such compression will be seen.

Seborrheic Dermatitis

Seborrheic dermatitis is a skin condition that mainly affects the scalp, causing scaly patches of red skin along with stubborn dandruff. It is easily mistaken for scalp psoriasis and vice versa.

With seborrheic dermatitis, the dandruff flakes tend to be fine and slightly yellowish, while the scalp itself will be oily. With psoriasis, the flakes will be silvery-white with a lamellar (scale-like) appearance. Moreover, psoriatic skin will invariably be dry.

As with eczema, the conditions can be differentiated under the microscope by their acanthotic or non-acanthotic appearance.

Pityriasis Rosea

Pityriasis rosea is a benign skin condition whose name is derived from the Latin for "fine pink scale." It generally starts with a large, slightly raised, scaly patch—called a herald patch—on the back, chest, or abdomen. The herald patch is typically followed by the appearance of smaller patches that sweep outward like the boughs of a pine tree.

This characteristic rash pattern is usually enough to differentiate pityriasis rosea from psoriasis. Psoriatic plaques also tend to be far more irregular in shape with a more pronounced scaling. Pityriasis rosea usually resolves completely within six to eight weeks; psoriasis is characterized by recurrent flares.

Lichen Planus

Lichen planus, a skin condition thought to be autoimmune, causes swelling and irritation in the skin, hair, nails, and mucous membranes. When it appears in the mouth, vagina, or other mucosal tissues, lichen planus can create lacy white patches. Lichen planus will typically manifest with psoriasis-like lesions on the wrists and limbs.

Lichen planus can be differentiated by the appearance of the skin lesions, which are thick like psoriasis but more purplish in color and lacking the characteristic scales. Moreover, it can affect mucosal tissues where psoriasis won't.

Under the microscope, psoriasis and lichen planus both have an acanthotic appearance. But, with lichen planus, there will be a band-like area of damage between the upper layer of skin (epidermis) and the middle layer (dermis).

Onychomycosis

Onychomycosis, also known as tinea unguium, is a fungal infection of the nails. Nail psoriasis is frequently mistaken for onychomycosis given that they have similar symptoms, namely the thickening, crumbling, and lifting of the nail plate, as well as the formation of abnormal ridges and dents.

One of the first clues that a nail disorder is psoriatic is the appearance of skin plaques elsewhere on the body. To confirm the suspicion, a dermatologist will take a scraping from the nail and examine it under the microscope. If there are no fungal spores, it can reasonably be assumed that psoriasis is the cause.

Psoriasis Doctor Discussion Guide

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Lupus

Systemic lupus erythematosus, also known as lupus, is an autoimmune disease affecting multiple organ systems, including the skin.

One of the tell-tale signs of lupus is a rash formation on the cheeks and nose, known as the butterfly rash. When lupus affects the skin specifically—a condition known as discoid lupus erythematosus—the lesions will be far less scaly than psoriasis and lack the lamellar appearance.

Doctors can usually confirm lupus with a series of blood tests, including the antinuclear antibody (ANA) test. Skin biopsy, including the use of direct and indirect immunofluorescent tests, can also confirm lupus as the cause.

Squamous Cell Carcinoma

Squamous cell carcinoma is the second most common type of skin cancer. Manifesting with thick, flat, scaly nodules, it is usually found on areas of the body damaged by ultraviolet (UV) rays from the sun or tanning beds.

Squamous cell carcinoma can mimic psoriasis but tends to be less scaly and limited to areas of sun-damaged skin. Generally speaking, there will only be a handful of cancerous lesions.

Squamous cell carcinoma can readily be diagnosed with a skin biopsy. While psoriasis will demonstrate the proliferation of keratinocytes (a type of skin cell found in abundance throughout the epidermis), squamous cell carcinoma will have a proliferation of squamous cells (the type found mainly on the outer part of the epidermis).

Mycosis Fungoides

Mycosis fungoides, also known as Alibert-Bazin syndrome, is the most common form of cutaneous T-cell lymphoma—a dermatological variation of a blood cancer known as non-Hodgkin lymphoma.

Mycosis fungoides manifests with rash-like patches of skin. In the early stages, the lesions will appear scaly and often be extremely itchy. The buttocks is often the first part of the body affected. Over time, the lesions can develop elsewhere, causing widespread redness and itching, but far less scaling.

Mycosis fungoides is easily confused with psoriasis in the early stages. Unlike psoriasis, mycosis fungoides is often accompanied by persistently swollen lymph nodes. Pancreas and liver enlargement are also common.

A skin biopsy can help differentiate the diseases. With mycosis fungoides, the biopsied tissue will have microscopic pus-filled cavities in the epidermal layer, known as Pautrier abscesses.

A Word From Verywell

Clearly, the problem with misdiagnosis is that it can expose you to unnecessary and unhelpful treatments. Worse yet, by assuming it's psoriasis without exploring other possible causes, the signs of a potentially more serious illness can be missed. This is why self-diagnosing psoriasis is never a good idea. If you are worried about a skin condition, ask your doctor for a referral to a dermatologist. Mention both skin- and non-skin-related symptoms, as doing so increases your chance of reaching the correct diagnosis.

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