Erythema multiformehttps://en.wikipedia.org/wiki/Erythema_multiforme
Erythema multiforme est conditio cutis, quae cum ruboribus inaequalibus evoluta in “scopum laesionum” (typice laesio in ambobus manibus occurrit). Erythema fortasse per infectionem vel medicamentum nuditatis mediatur.

Conditio variat a forma levi, per se limitata, ad formam gravem, vitam minacem, quae nota est ut erythema multiforme maior, quod etiam membranas mucosas implicat. Involvement membranae mucosae vel bullarum signa gravitatis sunt.

- Erythema multiforme minor: placae typicae vel elevatae, papulae edematosae acriter distributae.
Forma levia solet cum scabellis levibus (sed pruritus valde intensus), maculis roseo‑rubentibus, aequaliter distributis, a membris extremis incipiens. Resolutio levitatis intra 7‑10 dies est typica in hac forma morbi.

- Erythema multiforme major: placae typicae vel elevatae, papulae edematosae acriter distributae cum implicatio unius vel plurium membranarum mucosarum. Pars epidermidis involvit minus quam 10 % totius superficiei corporis.

Curatio OTC Medicamenta
Si febris est (tempus corporis elevatum), commendatur ut quam primum medicum videat.
Medicamina suspecta suspendenda sunt (e.g. antibiotica, anti‑inflammatoria non‑steroidea).
Antihistaminica oralia, ut cetirizine et loratadine, ad pruritum.
#Cetirizine [Zytec]
#LevoCetirizine [Xyzal]
#Loratadine [Claritin]
☆ In anno 2022 Stiftung Warentest ex Germania provenit, satisfactio consumptoria cum ModelDerm paulo minus fuit quam cum consultationibus telemedicinis solutis.
  • Erythema multiforme minor ― Nota quod centra laesiones albas esse possunt.
  • Target laesiones in crure
  • Urticaria etiam considerari potest ut diagnosis differentialis.
  • Target laesio Erythema multiforme Potest etiam esse primum indicium DECEM, quod diffunditur pusulae.
  • Manifestatio typica erythema multiforme
  • Morbus lyma quoque habendus est. cf) Bulls eye of Lyme Disease Rash
References Recent Updates in the Treatment of Erythema Multiforme 34577844 
NIH
Erythema multiforme (EM) est conditio in qua maculae propriae scopo‑similes apparent in utraque cute et membrana mucosa ob reactiones immunes. Etsi saepe a viribus contagiosis, praesertim herpes simplex virus (HSV), vel a quibusdam medicamentis, causa in multis casibus ignota manet. Acutum EM tractatur intendens ad levandam symptomata utens corticosteroids vel antihistamines. Administratio frequens EM est efficacissima, cum unicuique patienti regimen proprium formandum est. Primae aditus includunt curationes orales et topicas. Haec includunt corticosteroids et medicamenta antivirals. Therapiae generales constant a fortibus cremoribus steroidalibus et solutionibus pro membranis mucosis affectis. Patientibus male toleranti antivirals, secundae lineae optiones includunt medicamenta immunosuppressiva, antibiotics, anthelmintics et antimalarials.
Erythema multiforme (EM) is an immune-mediated condition that classically presents with discrete targetoid lesions and can involve both mucosal and cutaneous sites. While EM is typically preceded by viral infections, most notably herpes simplex virus (HSV), and certain medications, a large portion of cases are due to an unidentifiable cause. Treatment for acute EM is focused on relieving symptoms with topical steroids or antihistamines. Treatment for recurrent EM is most successful when tailored to individual patients. First line treatment for recurrent EM includes both systemic and topical therapies. Systemic therapies include corticosteroid therapy and antiviral prophylaxis. Topical therapies include high-potency corticosteroids, and antiseptic or anesthetic solutions for mucosal involvement. Second-line therapies for patients who do not respond to antiviral medications include immunosuppressive agents, antibiotics, anthelmintics, and antimalarials
 Use of steroids for erythema multiforme in children 16353829 
NIH
In multis casibus, mitis erythema multiforme sua sponte intra 2‑4 septimanas resolvit. Stevens‑Johnson syndrome, gravis condicio membranis mucosarum afficiens, usque ad sex septimanas durare potest. Steroids non sunt typice commendati in casibus levibus. Utrum steroids adhibeantur in erythema multiforme gravi, incertum est, cum nulla sint clara inventa ex studiis incertis adhibitis, quibus patientibus hac curatione prodesset.
In most cases, mild erythema multiforme is self-limited and resolves in 2 to 4 weeks. Stevens-Johnson syndrome is a serious disease that involves the mucous membranes and lasts up to 6 weeks. There is no indication for using steroids for the mild form. Use of steroids for erythema multiforme major is debatable because no randomized studies clearly indicate which children will benefit from this treatment.
 Drug-induced Oral Erythema Multiforme: A Diagnostic Challenge 29363636 
NIH
Casus oralis erythema multiforme (EM) a TMP/SMX causatus exhibetur, ostendens ulcera typica oris et labii, sine laesionibus cutis. Hoc sapienter opus est distinguere a morbis ulcerativis oris aliis. Aegrotus curam symptomaticam et tabulas prednisolone accepit, quod duxit ad emendationem cum cessatione TMP/SMX.
We report a case of oral erythema multiforme (EM) secondary to TMP/SMX that presented with oral and lip ulcerations typical of EM without any skin lesions and highlights the importance of distinguishing them from other ulcerative disorders involving oral cavity. The patient was treated symptomatically and given tablet prednisolone. The condition improved with stoppage of TMP/SMX therapy.
 Erythema Multiforme: Recognition and Management. 31305041
Erythema multiforme est reactio quae cutem et interdum mucosas implicat, systemate immunitario utitur. Typice manifestat laesiones clypeo‑similes, quae separatim apparent, recurrunt vel perseverant. Haec laesiones praesertim extremas, praecipue superficies exteriores, afficiunt. Causae principales includunt infectiones, sicut herpes simplex virus et Mycoplasma pneumoniae, atque quaedam medicamenta, immunizationes et morbos autoimmunes. Distinguere erythema multiforme a urticaria per durationem laesionum: laesiones erythema multiforme saltem septem dies fixa manent, dum laesiones urticariae intra diem saepe evanescunt. Quamquam similis, interest a syndromo graviore Stevens‑Johnson, quod typice exhibet maculam erythematosam vel purpuricam cum pustulis disseminatis. Administratio erythema multiforme includit subsidia symptomatica cum steroidibus topicis vel antihistaminicis, et tractatio causae subiectae. Pro casibus recurrentibus, cum herpes simplex virus coniunctis, therapia prophylactica antiviralis commendatur. Gravis implicatio mucosalis potest requirere hospitalizationem cum fluidis intravenosis et subsequenti correctione electrolyte.
Erythema multiforme is a reaction involving the skin and sometimes the mucosa, triggered by the immune system. Typically, it manifests as target-like lesions, which may appear isolated, recur, or persist. These lesions usually symmetrically affect the extremities, particularly their outer surfaces. The main causes include infections like herpes simplex virus and Mycoplasma pneumoniae, as well as certain medications, immunizations, and autoimmune diseases. Distinguishing erythema multiforme from urticaria relies on the duration of lesions; erythema multiforme lesions remain fixed for at least seven days, while urticarial lesions often vanish within a day. Although similar, it's crucial to differentiate erythema multiforme from the more severe Stevens-Johnson syndrome, which typically presents widespread erythematous or purpuric macules with blisters. Managing erythema multiforme involves symptomatic relief with topical steroids or antihistamines and addressing the underlying cause. For recurrent cases associated with herpes simplex virus, prophylactic antiviral therapy is recommended. Severe mucosal involvement may necessitate hospitalization for intravenous fluids and electrolyte replacement.