Dermatology: Practical and Conceptual


Research Letter | Dermatol Pract Concept. 2025;15(1):4929 1

Reflectance Confocal Microscopy  
of Sweet Syndrome

François Skowron1, Amélie Carbonnelle-Puscian2, Marco Ardigò3

1 Department of Dermatology, Hôpitaux Drôme Nord, Romans-Sur-Isère, France

2 Dermapath Network, Cypath, Villeurbanne, France

3 Department of Biomedical Sciences, Humanitas University, Milan, Italy

Key words: Confocal Microscopy, Neutrophilic Dermatosis, Biopsy, Diagnosis

Citation: Skowron F, Carbonnelle-Puscian A, Ardigò M. Reflectance Confocal Microscopy of Sweet Syndrome. Dermatol Pract Concept. 
2025;15(1):4929. DOI: https://doi.org/10.5826/dpc.1501a4929

Accepted: August 26, 2024; Published: January 2025

Copyright: ©2024 Skowron et al. This is an open-access article distributed under the terms of the Creative Commons Attribution-
NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, 
distribution, and reproduction in any medium, provided the original authors and source are credited.

Funding: None.

Competing Interests: None.

Authorship: All authors have contributed significantly to this publication.

Corresponding Author: François Skowron- Department of Dermatology, Hôpitaux Drôme Nord, 607 avenue Geneviève De Gaulle-
Anthonioz, 26102 Romans-Sur-Isère, France

Introduction

Sweet syndrome or acute febrile neutrophilic dermatosis is 

a rare disease, characterized by an acute onset of tender er-

ythematous plaques with dense neutrophilic infiltrate in the 

dermis [1].

Case Presentation

A 57-year-old woman developed multiple sore papules ini-

tially on the shoulders that within 3 days extended to the 

trunk, upper limbs, and thighs along with a mild fever 38°C. 

Her medical history revealed penicillin hypersensitivity 

and functional colonic disease. Papules were erythematous, 

edematous, enlarged up to 3 cm, and had a central darker 

area. Blood count, ionogram, C-reactive protein and renal 

function were normal. A papular lesion on the wrist was 

analyzed (Figure 1A). Dermoscopy showed homogenous vi-

olaceous pattern with some pinpoint reinforcements and a 

central purpuric zone (Figure 1B). Reflectance confocal mi-

croscopy (RCM) showed dark areas and numerous, single or 

aggregates, bright cellular structures of different shapes at 

the dermo-epidermal junction (Figure 2A) and some isolated 

bright cells surrounded by a dark acellular area at upper 

epidermal layers (Figure 2B). Biopsy revealed an acanthotic 

epidermis, intense papillary edema, and an intense poly-

morphous inflammatory infiltrate in the dermis composed 

mainly of neutrophils. There was no leukocytoclasia or vas-

culitis (Figure 1C). An idiopathic Sweet syndrome was diag-

nosed. The eruption resolved over 3 weeks with a regimen of 

systemic corticosteroid with progressive tapering. A work-up 

revealed no sepsis, no cancer, no hemopathy, or inflamma-

tory diseases.

Conclusions

Sweet syndrome (acute febrile neutrophilic dermatosis) is a 

rare disease affecting typically women in the third through 



2 Research Letter | Dermatol Pract Concept. 2025;15(1):4929

Figure 2. RCM findings: (A) Dark areas and numerous, single or aggregates, bright cells of 

different shape resembling polymorpho-nucleated cells (green arrow) at dermo-epidermal 

junction and (B) some isolated bright cells surrounded by a dark acellular area at upper 

epidermal layers.

Figure 1. Clinical findings: (A) Multiple erythematous papules with central darker area on the upper trunk 

and arms (green marker 01: recent papular lesion on the wrist analyzed). (B) Dermoscopy: homogenous 

violaceous pattern with some pinpoint reinforcements and a central purpuric zone. (C) Histological findings 

(H&E, original magnification ×10): intense papillary edema, and an intense polymorphous inflammatory 

infiltrate in the dermis composed mainly of neutrophils.

sixth decades [1]. The patient presents with a rapid onset 

of tender, sharply demarcated inflammatory papules on the 

face, upper chest and back, which spread over the trunk and 

limbs in a few days. Most cases are idiopathic, and some-

times they are associated with drug reaction, infection, 

cancer, or inflammatory diseases. Dense neutrophilic infil-

trate in the dermis without leukocytoclastic vasculitis is a 

major criterion for definite diagnosis of Sweet syndrome [2].  

Intense papillary edema is another frequent histologic 

feature. Reflectance confocal microscopy (RCM) is a 



Research Letter | Dermatol Pract Concept. 2025;15(1):4929 3

noninvasive diagnostic tool that evaluates the epidermis 

and papillary dermis at a cellular level. It has been shown 

that RCM is efficient in psoriasis in monitoring neutrophils 

which appear as bright round to oval cells surrounded by a 

dark acellular area [3]. Edema appears as dark homogenous 

area just below the epidermis [4]. In our case report, RCM 

allowed us to observe these 2 important histologic criteria: 

intense neutrophilic infiltrate and papillary edema. One limit 

of RCM is the inability to determine presence or absence of 

vasculitis. However, it seems that RCM findings with neu-

trophilic infiltrate and dermal edema, in a context of abrupt 

tender erythematous lesions on the upper trunk and limbs, is 

helpful in diagnosing Sweet syndrome and swiftly initiating 

corticosteroid systemic treatment.

Conclusion: RCM is useful for managing Sweet syn-

drome in real time.

References

1. von den Driesch P. Sweet’s syndrome (acute febrile neutrophilic 

dermatosis). J Am Acad Dermatol. 1994;31(4):535-56; quiz  

57-60. DOI: 10.1016/s0190-9622(94)70215-2. PMID: 8089280

2. Cohen PR. Sweet’s syndrome–a comprehensive review of an acute 

febrile neutrophilic dermatosis. Orphanet J Rare Dis. 2007;2:34. 

DOI: 10.1186/1750-1172-2-34. PMID: 17655751. PMCID:  

PMC1963326.

3. Wolberink EA, Peppelman M, van de Kerkhof PC, van Erp PE, 

Gerritsen MJ. Establishing the dynamics of neutrophil accumu-

lation in vivo by reflectance confocal microscopy. Exp Dermatol. 

2014;23(3):184-8. DOI: 10.1111/exd.12345. PMID: 24521061

4. Ardigo M, Agozzino M, Amorosi B, Moscarella E, Cota C,  

de Abreu L, et al. Real-time, non-invasive microscopic confir-

mation of clinical diagnosis of bullous pemphigoid using in 

vivo reflectance confocal microscopy. Skin Res Technol. 2014; 

20(2):194-9. DOI: 10.1111/srt.12105. PMID: 23981107