Introduction

Pustular psoriasis is a rare, chronic type of skin disorder that is distinguished by red skin with yellow pus-filled blisters known as pustules which can be widespread or localised to a certain region of the body.¹ Pustular psoriasis can develop through a combination of inherited traits and certain triggers such as medication, infection and stress. The disease affects adults primarily between ages 40-50 and also is present in children during infancy. Accurate diagnosis of pustular psoriasis is vital as it can be a potential life threatening condition that requires immediate treatment, if left untreated the disease can progress to develop more serious complications such as renal failure and sepsis.² This article delves into the key diagnostic approaches for pustular psoriasis including clinical examination, skin biopsy and differential diagnosis. 

Clinical examination

Patient history

Onset and duration of symptoms

The onset of pustular psoriasis is typically:

• Rapid: pustular psoriasis can develop quickly forming pustules within just one hour
• Systemic symptoms: pustular psoriasis can often be accompanied with systemic symptoms such as muscle weakness, fatigue and fever
• Recurrent flares: There could be recurrent episodes of pustular psoriasis followed by skin clearance between flares where there is an absence of symptoms
• First year onset: Sometimes the disease can progress within the first few weeks to a year after birth³

The duration of pustular psoriasis can range widely:

• Pustular psoriasis flares can last from several weeks to months and can occur several times a year to some or once every couple years for others
• Pustular psoriasis symptoms can be short term, intermittent or long lasting
• The frequency and severity of these pustules can vary being very severe to some whilst very mild in others. Most flares can last between 2-5 weeks, nevertheless, some can last for more than 3 months and around 50% of severe cases require hospitalisation³ 

Previous psoriasis diagnosis or family history

If you have a family history of pustular psoriasis, you are more prone to not only developing the disease but also having a significantly earlier onset to the condition compared to those without a family history of the disease.⁴ If you have pustular psoriasis there can be comorbidity with other types of psoriasis for instance plaque psoriasis where symptoms commonly appear on the elbows, knees, and scalp.⁵

Triggers of pustular psoriasis

Pustular psoriasis is an autoimmune disease which means that the body has an overactive immune system that targets healthy cells which eventually leads to inflammation and pustules.  There are also several factors that can trigger pustular psoriasis, this includes⁶:

1. Medication such as penicillin, lithium and the withdrawal of corticosteroids 
2. Viral and skin infections such as staphylococcus aureus are commonly reported in a high proportion of people with pustular psoriasis
3. Stress including emotional and psychological stress can trigger pustular psoriasis or worsen the condition
4. Pregnancy can trigger a condition called impetigo herpetiformis which is rare and life threatening.

Subtypes of pustular psoriasis

Generalised pustular psoriasis (GPP)

One of the most common types of pustular psoriasis is generalised pustular psoriasis (GPP)¹. In GPP the subtypes include:

• Von Zumbusch subtype which is a more severe, life threatening form where there are sudden pustules which appear all over the body and is often accompanied with systemic symptoms
• Annular subtype which is distinguished by annular lesions
• Exanthematic subtype, a short term eruption of a pustule with the absence of systemic symptoms that disappears after a couple of days
• Impetigo herpetiformis which is a type of GPP that occurs during the third trimester of pregnancy

Localised pustular psoriasis 

Another common type of pustular psoriasis is localised pustular psoriasis.¹ The subtypes include:

• Palmoplantar pustulosis (PPP) where pustules are found in soles of the feet and palms of hands
• Acrodermatitis continua of Hallopeau (ACH) where pustules affect the toes, fingers, and nails

Skin biopsy

Purpose of biopsy

If you have pustular psoriasis, a skin biopsy can be undergone to help confirm the diagnosis and eliminate any other potential conditions which have similar symptoms. For instance, pustular psoriasis can often be misdiagnosed with other conditions like eczema or acute generalised exanthematous pustulosis (AGEP). Having a biopsy will allow a pathologist to analyse a sample of your skin under a microscope and will allow them to check for specific features that are found in pustular psoriasis. A biopsy can also be useful to help differentiate subtypes of psoriasis and make sure that the right treatment is used.⁷

Histopathological features

To confirm if a diagnosis is pustular psoriasis via a skin biopsy there are several histopathological features that can differentiate pustular psoriasis from other conditions. Some features of pustular psoriasis include:

• The presence of a large proportion of neutrophils in the papillary dermis and epidermis¹
• The presence of spongiform pustules of kogoj which are identified as very tiny pus filled pockets in the epidermis which are made by a large proportion of neutrophils and keratinocyte edema
• A cluster of neutrophils in the stratum corneum known as Munro’s Microabscesses which is a key feature in pustular psoriasis

Differential diagnosis

The differential diagnosis of pustular psoriasis¹ are:

Key distinguishing features for differential diagnosis

Onset speed and systemic symptoms 

Pustular psoriasis is most commonly misdiagnosed with AGEP. Pustular psoriasis has a rapid onset, it occurs suddenly and is accompanied with systemic symptoms. However, with conditions, such as AGEP, although it also has a rapid onset it is a drug induced condition that develops quickly after starting a new medication. The severity of symptoms for AGEP is more severe than pustular psoriasis and can lead more frequently to hospitalisation, which can facilitate in differentiating it from pustular psoriasis.⁸

Distribution and pattern of pustules

In pustular psoriasis, the pustules are usually located in areas such as palms of hands, soles of feet, and can sometimes be widespread across the body. The location and pattern of these pustules can help to distinguish pustular psoriasis from other conditions. For instance, AGEP presents with widespread pustules, however these are scattered across the skins and can be found in areas that are not found in psoriasis.⁸ 

Microbial cultures 

Microbial cultures can be used to identify if the pustules are caused by bacterial or fungal infection rather than an autoimmune response. The pustules formed from pustular psoriasis are usually sterile which means they are not caused by an infection. Nonetheless, infections or fungal conditions such as impetigo can cause pustules which can be identified using microbial cultures. If the culture has a negative result for fungi or bacteria this can help with the diagnosis of pustular psoriasis or allow further investigations to be carried out.⁹

Response to treatment

Pustules respond differently to various treatments and this can be a key differentiator in diagnosis pustular psoriasis. AGEP conditions usually improve after the triggering factor is eliminated whereas pustular psoriasis responds with treatments such as immunosuppressants. The time frame and the different responses to treatment can aid in differentiating these conditions allowing for a more accurate diagnosis.¹⁰

FAQ’s

Is pustular psoriasis contagious?

No. Pustular psoriasis is an autoimmune chronic condition and is not caused by a viral or bacterial infection. The pustules are sterile and therefore are not contagious.¹ 

How urgent is the treatment for GPP?

GPP is a serious medical condition and if left untreated can lead to hospitalisation due to more serious complications such as renal failure and sepsis.² 

When is a skin biopsy necessary for pustular psoriasis?

A skin biopsy may be recommended to rule out other similar conditions when a clinical diagnosis is uncertain. Histological features such as spongiform pustules of kogoj can help to confirm the diagnosis.¹

What causes pustular psoriasis?

Pustular psoriasis has a genetic component, if you have a family history of pustular psoriasis, you are more prone to developing the disease.⁴ There are several factors that can trigger pustular psoriasis including medication, skin infection, stress and pregnancy.⁶

Summary

Pustular psoriasis is a rare, chronic autoimmune condition that causes the presence of pustules across the skin. This includes generalised forms such as GPP which causes systemic symptoms with widespread pustules, and also localised forms like PPP which are found in specific regions of the skin. Diagnosing pustular psoriasis accurately requires a detailed clinical examination that involves the assessment of patient history, onset and duration of symptoms, and the distribution of pustules. When confirming a diagnosis, skin biopsies play a pivotal role by distinguishing histological features such as Munro’s Microabscesses and presence of spongiform pustules of kogoj. Differential diagnosis is important in differentiating pustular psoriasis from other similar conditions such as impetigo and AGEP; this can be distinguished by comparing onset speed, systemic symptoms and using microbial cultures. When implemented together these diagnostic steps can ensure a more accurate diagnosis of pustular psoriasis and can help clinicians to provide more effective treatment strategies to manage pustular psoriasis.