A review of 185 cases of monkeypox, published in the British Journal of Dermatology, has found that the main features of the current outbreak of monkeypox cases differ from past cases. Crucially, the research found that the main symptom of the current outbreak is not pustules (pus-filled lesions), as previously described, but much rarer and more notable, pseudo-pustules.

The research, conducted by a network of Spanish dermatologists, collected and categorised the key features of the current monkeypox outbreak. All dermatologists in Spain were invited to contribute cases to the study. The 185 cases studied represent 9% of those reported to the Spanish national surveillance system by the 11th of July 2022.

Unique skin symptoms

Typical monkeypox symptoms include fever and swelling of the lymph nodes, followed by a generalised rash that progresses through four distinct stages. While fever and lymph node swelling remain common in this outbreak, the research found that cases tend to feature few skin lesions, sometimes appearing only in a single area.

Most cases started on the genitals, face, arms, hands, and perianal area. Previous research into this outbreak has described these lesions as pustules, or pus-filled lesions. Crucially, however, this research has discovered that the lesions are actually pseudo-pustules.

These pseudo-pustules are similar in appearance to pustules, but are actually whitish, solid papules (raised lesions). With real pustules it is possible to scrape away the top layer of the lesions to access the pus, with pseudo-pustules it is not possible to do this. Over time, these pseudo-pustules can become necrotic and lead to ulcers. This information is important as very few diseases produce these pseudo-pustules.

Other skin symptoms include:

• Ulcers where the pseudo-pustules meet the moist, inner linings of body cavities such as the nose, the mouth, or the genital areas, also known as mucous membranes. These mucosal ulcers can be the most common lesions in some cases
• Monkeypox whitlow, a painful infection of the finger
• A rash featuring blister-like lesions (vesicles) surround by a halo of inflammation leading to raised lesions (papules) that arrive after the initial skin lesions

Likely transmission route

The research also provides further evidence to support that a primary transmission route for this outbreak is via sexual contact rather than airborne particles. The localised skin lesions that characterise this outbreak support that theory in several ways:

• Suspected primary lesions were centred in most patients in areas of close contact during sexual intercourse, rather than the typical widespread rash. Related viruses (orthopoxviruses and parapoxviruses) usually cause localised skin lesions at the site that the disease enters the body and this is evidence that monkeypox follows a similar pattern
• The cases studied were comprised entirely of men who have sex with men. Though this may change over time, if the viral infection were through airborne particles, then the outbreak would be more likely to affect a more diverse population group

Dr Ignacio García Doval, the coordinator of the research from the Spanish Academy of Dermatology, said:

“A crucial aspect of managing a fast-moving disease outbreak is having as much information as possible. Our research shows that the symptoms of the current outbreak are unusual and there is evidence that this is due to skin-to-skin contact during sex. Rather than the typical widespread rash seen in past cases, recent cases tend to have far fewer skin lesions, often in one location. 

“It is particularly important for healthcare professionals to note the appearance of these skin lesions. Monkeypox is often described as causing pustules, pus-filled lesions, but in this outbreak, the main skin symptom is actually pseudo-pustules, white, solid papules which look like pustules, but which don’t contain any pus. This feature is very rare in other diseases, so is a very clear sign of monkeypox.

“No patient involved in this research died and hospitalisation was uncommon, however, the disease is very uncomfortable and can have long-term consequences, including scarring in visible areas.”

Dr John Ingram, Editor-in-Chief of the British Journal of Dermatology, said:

“This research contributes substantially to the knowledge we have of the current monkeypox outbreak. We hope that this will aid targeted public health messaging, and the swift diagnosis of people who are infected.

“The large sample size, which is likely to be representative of cases in Spain, makes this a particularly strong study. As does the fact that cases came from across the country and from different levels of the health system, including emergency rooms, STD clinics, and dermatology consultations.”

The researchers also found that well-controlled HIV did not seem to affect the severity of the disease.

The study includes a photographic atlas of categorised symptoms, to help healthcare professionals spot the signs of the condition.

Notes to Editors

For more information, please contact the media team: comms@bad.org.uk

Study Information

Monkeypox outbreak in Spain: clinical and epidemiological findings in a prospective cross-sectional study of 185 cases

The study will be available to find online here, after the embargo has lifted: https://onlinelibrary.wiley.com/doi/10.1111/bjd.21790

About the BAD

The British Association of Dermatologists (BAD) is the professional membership body for dermatologists in the UK. Founded in 1920, the BAD is a registered charity representing over 2,400 members, dedicated to medical education, professional practice and standards, and research in dermatology.

For further information about the charity, visit www.bad.org.uk.

About the BJD

The British Journal of Dermatology (BJD) is a top-ranked international dermatology journal, publishing the highest-quality research to advance the understanding and management of skin disease to improve patient outcomes. The BJD is one of the journals of the British Association of Dermatologists, the professional membership body for dermatologists in the UK.