Dermatology: Practical and Conceptual Letter to the Editor | Dermatol Pract Concept. 2022;12(4):e2022187 1 Unilateral Rosacea in a Patient With Multiple Sclerosis Mariem Tabka1, Rima Gammoudi1, Refka Frioui1, Nadia Fetoui1, Sana Mokni1, Amina Ounallah1, Colondane Belajouza1, Mohamed Denguezli1 1 Department of Dermatology, Farhad Hachad Hospital of Sousse, Sousse, Tunisia Citation: Tabka M, Gammoudi R, Refka F, et al. Unilateral Rosacea in a patient with multiple sclerosis. Dermatol Pract Concept. 2022;12(4):e2022187. DOI: https://doi.org/10.5826/dpc.1204a187 Accepted: March 17, 2022; Published: October 2022 Copyright: ©2022 Tabka 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: Refka Frioui, MD, Department of Dermatology, Farhat Hachad Hospital, Ibn Jazzar,4000 Sousse, Tunisia. Phone: +216 29320235; Email: rafkouna1993@gmail.com Written Consent from the patient: The authors certify that they have obtained all appropriate patient consent forms, in which the patient gave his consent for images and other clinical information to be included in the journal. The patient understands that his name and initial will not be published and due effort will be made to conceal his identity, but that anonymity cannot be guaranteed. Introduction Rosacea is a common and chronic inflammatory skin condition of clinical heterogeneity and intriguing pathophys- iological mechanisms. Herein, we report a case of unilateral rosacea in a patient with multiple sclerosis. Case presentation A 37-year-old woman presented to the dermatology department with a 2-year history of facial unilateral redness and paroxysmal pain. Over the last 2 years, she received multiple treatments, such as ivermectin cream, doxycycline and metronidazole gel, without any benefit. Her facial der- matosis presented as unilateral persistent erythema with multiple papules and pustules strictly confined to the right side (Figure 1). The skin biopsy revealed a perivascular and perifollicular inflammatory infiltrate consisting of lym- phocytes, neutrophils with the presence of demodex mites, compatible with rosacea. The unilateral distribution of the dermatosis was suggestive of pre-existing neurological le- sion. We referred the patient for additional testing, including an MRI of the brain, which demonstrated a demyelinating plaque at the trigeminal root entry zone consistent with tri- geminal neuralgia secondary to multiple sclerosis (Figure 2). She was put on natalizumab and bolus steroid therapy. The pain has decreased. However, the rosacea got worse, proba- bly because of corticosteroids. Conclusion Despite its high prevalence, the underlying pathophysiology of rosacea remains unclear. This observation highlights the complexity of the disease contributing mechanisms. Indeed, it describes a distinct variant of the disease denominated neurogenic rosacea, presented with unilateral arrangement and associated with an autoimmune disease. The patho- physiological mechanisms implicated in the development of 2 Letter to the Editor | Dermatol Pract Concept. 2022;12(4):e2022187 rosacea include dysregulation of the innate immune system, imbalance of commensal skin microbiota, and abnormal neurovascular signaling [1]. Neurogenic rosacea, a recently described rosacea subtype, demonstrates the role of local neural-associated mediators dysregulation in the patho- physiology of the dermatosis [2]. Moreover, it occurs more often in patients with neurological or neuropsychiatric con- ditions, including complex regional pain syndrome, essential tremor, depression and obsessive-compulsive disorder [2]. Dysesthesia secondary to neuronal injury was commonly re- ported and was associated with classical rosacea signs [2]. It is well known that patients suffering from rosacea have an increased of developing a number of auto-immune dis- eases, including multiple sclerosis. Yet, it is also important to notice that trigeminal neuralgia, attributed to multiple sclerosis, may explain the neurogenic inflammation leading to such skin condition as well as the unilateral arrangement of the lesions. Our case may also reflect a regional desta- bilization of the neuroimmunocutaneous system induced by multiple sclerosis. This hypothesis fully represents the con- cept of immuno-compromised district (ICD) [3,4]. ICD, a newly introduced pathogenic concept, stipulates that several different factors are likely to create a privileged cutaneous district, which explains the segmental presentation of many skin disorders, including bullous pemphigoid, pemphigus, lichen planus, discoid lupus erythematosus, drug eruptions and acne [4-6]. Trigeminal neuralgia attributed to multiple sclerosis, in analogy with the aforementioned facial nerve palsy, could locally alter the immune response and induce the occurrence of rosacea following the neurologically im- paired facial side. Regardless of the etiopathogenic mechanisms of rosacea, the interaction between the skin and the immune and ner- vous systems is currently well established, with rosacea being one of the established examples involving these var- ious systems. The systematized arrangement of a dermato- sis that is strictly confined to a specific area may refer to Figure 1. (A) Unilateral rosacea confined to the right hemiface. (B) Right lateral aspect evidencing erythema and papulopustules. (C)_Slight erythema on the left side. Figure 2. Neuroimaging findings in our patient with gadolinium-enhanced T1-weighted image on the axial plane that shows a hyperintense pontine lesion at the right trigeminal nerve zone. Letter to the Editor | Dermatol Pract Concept. 2022;12(4):e2022187 3 the “immunocompromised district” concept, and thus pro- moting investigations into possible immunocompromising factors. Further research is clearly needed to better describe the underlying patho-physiologic characteristics and to iden- tify additional effective treatment methods”. Acknowledgment: We thank the patient for granting permis- sion to publish this information (the patient in this manu- script has given written informed consent to publication of her case details). We are also indebted to Badreddine Sriha, MD, PhD, Department of Pathology, Farhat Hached Hospital, University of Sousse, for his interpretation of the skin biopsies. He received no compensation for his contributions. References 1. Choi JE, Di Nardo A. Skin Neurogenic inflammation. Semin Immunopathol. 2018;40(3):249-259. DOI: 10.1007/s00281- 018-0675-z. PMID: 29713744. PMCID: PMC6047518. 2. Scharschmidt TC, Yost JM, Truong SV, Steinhoff M, Wang KC, Berger TG. Neurogenic Rosacea: A Distinct Clinical Subtype Requiring a Modified Approach to Treatment. Arch Dermatol. 2011;147(1):123-126. DOI: 10.1001/archdermatol.2010.413. PMID: 21242409. PMCID: PMC3692271. 3. Egeberg A, Hansen PR, Gislason GH, Thyssen JP. Clustering of autoimmune diseases in patients with rosacea. J Am Acad Derma- tol. 2016;74(4):667-672.e1. DOI: 10.1016/j.jaad.2015.11.004. PMID: 26830864. 4. Ruocco V, Ruocco E, Piccolo V, Brunetti G, Guerrera LP, Wolf R. 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