Overview

Skin conditions show great variation in the size, shape, colour and location of the presenting issue.¹ This makes it difficult for doctors to give a correct diagnosis and distinguish skin conditions from others that show similar abnormalities. It is important for skin conditions to be accurately diagnosed to deliver appropriate treatments, reduce transmission of contagious conditions or to address a wider health concern. Pustular Psoriasis is a type of skin condition that is rare in the population, commonly leading to it being misdiagnosed.² It is a complicated disease that requires serious treatment, meaning diagnosis and medical care are crucial.² This article aims to aid with awareness of this disease by explaining how pustular psoriasis differs from other common skin conditions. 

What is Pustular Psoriasis? 

Symptoms of Pustular Psoriasis 

Pustular psoriasis is a subtype of the skin condition, psoriasis.³ Psoriasis describes when the skin gets inflamed and dry, particularly on the scalp, elbows or knees.⁴ This is a chronic condition that happens when the immune system is more active than normal, which can cause skin cells to grow and multiply rapidly.⁴ The term pustular means that this type of psoriasis produces pustules, small pus-filled lesions that are yellow/white in colour and painful³. There are two forms of pustular psoriasis, which depend on where the pustules form in the body. Localised pustular psoriasis can be seen to mostly affect skin on the hands or feet.³ However, generalised pustular psoriasis (GPP) is more likely to form all over wider areas of the body.² Generalised pustular psoriasis also causes a range of other symptoms, including a fever, chills and fatigue and causes complications such as sepsis and renal failure.²

Causes of Pustular Psoriasis 

Pustular psoriasis is a complicated disease where the exact cause of the condition is unknown.³ However, there is a range of factors that are linked to pustular psoriasis.³ Changes to an individual's DNA, known as genetic mutations, that affect the immune and inflammatory systems have been shown to be linked to pustular psoriasis.⁵ An example of this is having increased amounts of the HLA-B27 gene.⁶ Medications can also be connected to increasing the chances of developing pustular psoriasis, including some topical steroids and antimicrobial medicines such as amoxicillin.^3,5 Stopping medications suddenly can also trigger this.⁶ Other factors that are linked to the onset of pustular psoriasis are pregnancy, certain vaccinations (H1N1), skin infections and exposure to lots of ultraviolet light from the sun.^5,6

Diagnosis of Pustular Psoriasis 

To diagnose pustular psoriasis, a doctor will have to perform a physical examination involving checking the skin, as well as nails and mouth, for visible signs of skin abnormalities.⁶ A medical history will also be taken, including any symptoms that are being experienced.⁶ Several medical tests can be conducted to support diagnoses, including taking a blood sample and checking if there are abnormal quantities of white blood cells or increased amounts of inflammatory proteins (C-reactive protein) and immune proteins (immunoglobulins).⁷ A urine sample can be tested for increased rates of albumin (a protein found in the blood).⁷

Pustular Psoriasis vs Eczema 

What is Eczema? 

Eczema is also an inflammatory condition that produces skin abnormalities such as dry skin, rashes and itchy skin.⁸ Symptoms tend to differ from patient to patient and vary in appearance across age ranges.⁸ There are also different subtypes of eczema. For example, dyshidrotic eczema can form blisters and scaly areas of skin, most commonly on the hands and feet.⁸ Furthermore, nummular eczema produces yellow fluid-filled patches that can ooze and become crusty.⁸ These symptoms mean that pustular psoriasis and eczema can look very similar. 

Differentiating Pustular Psoriasis from Eczema 

There are some slight differences between the two diseases that can help distinguish the two. Pustular psoriasis tends to form on the soles of feet and the palms of hands, whereas eczema most often appears behind the knees or elbows.⁹ While there are types of eczema that produce blisters and fluid, these are normally clear in colour instead of the yellow pustules that form in pustular psoriasis.¹⁰ The two skin conditions react differently to medications such as steroids. While topical steroids are prescribed for eczema and can relieve symptoms, these medications can make symptoms of pustular psoriasis flare up and worsen.¹⁰

To support an accurate diagnosis, medical tests should be performed. A skin biopsy (removing a small portion of skin) is normally conducted on the pustules or blisters that have formed due to these conditions.¹⁰ When studied under a microscope, this can show swelling between skin cells and a buildup of fluid known as spongiotic tissue.¹¹ A biopsy of pustular psoriasis would show white blood cells gathering near the outer layer of skin.⁷ Studying the outer layer of skin under the microscope would also show abnormal contents of the cell structure or a thicker layer than normal for eczema.⁷

While there are some visible differences in eczema and pustular psoriasis, the fact that their symptoms are very similar means laboratory testing can be helpful when distinguishing the two of these skin conditions. 

Pustular Psoriasis vs Impetigo 

What is Impetigo? 

Impetigo is a skin condition caused by a bacterial infection that can spread from person to person easily and is highly contagious.¹² This causes yellow pustules and crusted patches of skin that are painful and itchy and mainly on the face.¹³ This skin condition differs from eczema and pustular psoriasis since its primary cause is being infected with a type of bacteria known as Staphylococcus aureus or Streptococcus pyogenes.¹³

Differentiating Pustular Psoriasis from Impetigo 

A visible feature that makes impetigo different from pustular psoriasis is the appearance of the pustules, which are commonly described as golden or brown for impetigo.¹³ Impetigo is more likely to affect young children, especially those living in countries with warm temperatures,¹² whereas pustular psoriasis can affect people of a range of ages and climates. Impetigo is more likely to form at sites of the skin that have been bitten by insects or injured by trauma.¹³ Impetigo will form at one site but can spread and form smaller pustules at other sites, known as satellite patches.¹² These features differentiate impetigo from pustular psoriasis, it a condition that can be diagnosed from visual examination. 

Given the fact that bacteria is the cause of impetigo it is easily differentiated from pustular psoriasis through laboratory tests. This is done through a bacterial culture test to detect strains of Staphylococcus aureus, especially if it was assumed the infection was resistant to antibiotics.¹²

Pustular Psoriasis vs Pustular Dermatoses 

What is Pustular Dermatoses? 

Subcorneal pustular dermatosis is a rare skin condition that produces pustules over a long period of time.¹⁴ These lesions mainly appear on the central trunk of the body (the chest and abdomen) and areas where the skin creases, such as the armpits, inside the elbows and behind the knees.¹⁵ Pustular dermatosis rarely forms on the face.¹⁵ The pustules formed in pustular dermatosis appear yellow at the base with a clear layer on top of them.¹⁵ These lesions tend to form in patterns that resemble a ring or wave.¹⁵

Differentiating Pustular Psoriasis from Pustular Dermatosis

Generalised pustular psoriasis and pustular dermatosis are very similar conditions and can be misdiagnosed for each other.¹⁴ When samples of the pustules are collected in a skin biopsy and studied under a microscope, these two conditions show varying features. The layers of skin in pustular psoriasis show collections of white blood cells; however, this is not seen in cases of pustular dermatosis.^7,14 The layers of skin below the pustules appear to show few abnormalities in structure or composition.¹⁴

Summary

Pustular psoriasis is a skin condition that forms red and itchy patches of skin with pustules that can flare up over the lifetime of the individual. The generalised subtype of this disease can lead to serious side effects that require urgent medical treatment. Therefore, it is important to accurately diagnose this condition so appropriate support can be provided. There are many other skin conditions that show similarities to pustular psoriasis, such as eczema, impetigo and pustular dermatosis. These conditions can cause similar symptoms and also produce pustules. While there are some differences in colour and location that can be useful in diagnosis, blood tests and biopsies can lead to accurate diagnoses. Increased genetic screening for pustular psoriasis is proposed for the future to link individuals to the skin condition and make diagnosis easier.