a 5-year - old , spayed female , indoor - only domestic shorthair cat was referred with an acute history of multifocal cutaneous and mucocutaneous erosive - ulcerative lesions and skin detachment . erosive - ulcerative and occasionally crusted lesions were apparent on the medial and lateral canthus of both eyes , ventral neck , abdomen , perivulvar region , periungual skin and medial aspect of the front and hindlimbs . diffuse and severe exfoliation was present on the dorsum and tail base and in both external ear canals . histopathological examination revealed extensive epidermal ulceration , interface dermatitis with vacuolar degeneration , apoptosis at multiple epidermal levels and basal , suprabasal and spinous dermoepidermal detachment . the histopathological diagnosis was consistent with stevens  johnson syndrome / toxic epidermal necrolysis ( sjs / ten ) . the recently reported algorithm of drug causality in epidermal necrolysis ( alden ) , currently used in human medicine , was applied and a score of + 6 was calculated ; this supported the view that sjs / ten in this cat was very likely to be associated with cefadroxil administration . this clinical communication reports cefadroxil as a very probable cause of sjs / ten in a cat ; the alden was applied in this case and supported diagnosis . stevens  johnson syndrome ( sjs ) and toxic epidermal necrolysis ( ten ) are variants of a spectrum of immune - mediated diseases , which also includes erythema multiforme ( em ) minor and major . in people , sjs and ten are caused by drugs in the vast majority of cases , while em is usually due to viral infections , mostly herpes simplex . for this reason , sjs and ten are often referred to as one entity ( sjs / ten ) , while em is considered a separate disease . recently , an algorithm to assess drug causality in human cases of sjs / ten has been proposed ( algorithm of drug causality in epidermal necrolysis [ alden ] ) , and proved to be very sensitive in comparison with case - control studies . the alden has also been used in a series of cases of ten in dogs . in animals , the aetiological classification of this group of diseases is not as well - defined , and the diagnosis is currently based on clinical criteria , which can be useful to differentiate em from the more severe forms , sjs and ten . histopathological examination , in most cases , can not clearly distinguish between em , sjs and ten , as the microscopic features of the different conditions often overlap . according to a recent review , em cases in cats are associated with feline herpesvirus infections , as well as administration of antibiotics and aurothioglucose . ten , or sjs / ten , has been rarely reported in cats and it has invariably been associated with drugs , such as flea dips containing d - limonene , feline leukaemia virus ( felv ) antiserum , cefaloridine , hetacillin , ampicillin , griseofulvin , penicillin , aurothioglucose and cephalexin . currently , sjs and ten in animals are believed to be analogues of the human diseases , while the same can not be stated of em . the aim of this case report is to describe the clinical and histological features of a feline case of sjs / ten and to evaluate drug causality in this cat by means of the alden . a 5-year - old , spayed female , indoor - only domestic shorthair cat was referred with an acute history of multifocal cutaneous and mucocutaneous erosive - ulcerative lesions and skin detachment . the lesions were rapidly worsening and occurred on the seventh day of therapy with cefadroxil ( cefacure tabs ; msd animal health ) 25 mg / kg po q24h , prescribed by the primary veterinarian for vomiting and diarrhoea of unknown origin . according to the owner , the cat had no history of exposure to any other medication or toxin . on general physical examination , the cat was 3% dehydrated , its heart rate was 250 bpm and its temperature was 39.6c . on dermatological examination , there were large areas of erosion / ulceration due to epidermal detachment affecting the ventral neck , abdomen , vulvar lips and perivulvar region , periungual skin and medial aspect of the front and hindlimbs ( figures 1 and 2 ) ; the footpads were unaffected . erosive - ulcerative and crusted lesions were apparent on the medial and lateral canthus of both eyes ( figure 3 ) . diffuse and severe exfoliation was present on the dorsum and tail base and in both external ear canals . erosive - ulcerative lesions on the ventral abdomen , perivulvar region and medial aspect of the front and hindlimbs of a 5-year - old , spayed female domestic shorthair cat close - up of an erosive - ulcerative lesion due to epidermal detachment on the ventral abdomen erosive - ulcerative and crusted lesions on the medial and lateral canthus of both eyes differential diagnoses for this presentation were adverse drug reaction , em major , sjs / ten , vasculitis , pemphigus vulgaris , bullous pemphigoid and exfoliative dermatitis secondary to thymoma . complete blood cell count revealed leukocytosis ( 22.86  10/l ; reference interval [ ri ] 2.8717.02  10/l ) , neutrophilia ( 13.05  10/l ; ri 1.4810.29  10/l ) with toxic changes and lymphocytosis ( 8.06  10/l ; ri 0.926.88  10/l ) . mmol / l ) , hypertriglyceridaemia ( 1.42 mmol / l ; ri 0.220.92 mmol / l ) and increased serum aspartate aminotransferase ( 41.38 u / l ; ri 1535 ) . serologies for felv and feline immunodeficiency virus were both negative , and thoracic radiographs and abdominal ultrasound examination did not show any abnormality . skin biopsies were taken with a 6 mm punch and samples were fixed in 10% buffered formalin . sections were paraffin - embedded and stained with haematoxylin - eosin , following standard procedures . histopathological examination revealed extensive epidermal ulceration , interface dermatitis with vacuolar degeneration , apoptosis at multiple epidermal levels and basal , suprabasal and spinous dermoepidermal detachment . there was a subepidermal mononuclear infiltrate , hair follicle telogenisation and atrophy , and a lymphocytic infiltrate was apparent in the follicular infundibulum ( figures 47 ) . light photomicrograph of a section of affected skin , showing suprabasal epidermal detachment and follicular atrophy . no sebaceous glands are detected ( haematoxylin and eosin , bar = 200 m ) light photomicrograph of a section of affected skin , showing apoptotic cells at various levels of the epidermis , vacuolar degeneration of basal cells and subepidermal mononuclear infiltrate ( haematoxylin and eosin , bar = 50 m ) epidermal necrosis due to confluence of multiple apoptotic cells ( haematoxylin and eosin , bar = 50 m ) lymphocytic infiltrate in the follicular infundibulum ( haematoxylin and eosin , bar = 50 m ) the histopathological diagnosis was consistent with sjs / ten . the recently reported algorithm for alden , currently used in human medicine , was applied to this case and a score of + 6 was calculated , meaning that sjs / ten in this cat is very likely to be associated with cefadroxil administration ( table 1 ) . details of the algorithm of drug causality for stevens  johnson syndrome ( sjs)/toxic epidermal necrolysis ( ten ) ( algorithm of drug causality in epidermal necrolysis ) applied to the case modified from sassolas et al < 0 , very unlikely ; 01 , unlikely ; 23 , possible ; 45 , probable ; 6 , very probable the cat was hospitalised and treated with intravenous fluids ( ringer s lactate 7.5 ml / h ) , marbofloxacin ( marbocyl ; vetoquinol ) 2 mg / kg iv q24h and methadone hydrochloride ( synthadon ; ati ) 0.2 mg / kg iv q6h to control cutaneous pain . the dermatological lesions worsened rapidly , leading to > 30% of the body surface affected by skin detachment . the cat became anorexic , severely depressed and hypothermic ( 36.2c ) and after 4 days of hospitalisation , the owner elected euthanasia for the cat . sjs / ten is a rare , acute , life - threatening reaction affecting the skin and mucosae , characterised by extensive necrosis and detachment of the epidermis , observed in people , dogs and cats . an algorithm of drug causality ( alden ) is currently used in human medicine to assess a very unlikely role of a drug , in order to clearly identify in each patient not only which molecule probably caused the reaction , but also which medications could safely be administered to the patient . in veterinary medicine , alden has been recently applied to a series of canine ten cases , and a probable causality for carprofen in a dog was established . to our knowledge , in this case alden was applied for the first time in a feline patient . in the cat of this report very probable causality for sjs / ten was assigned to cefadroxil , a first generation cephalosporin , according to the + 6 score obtained . the 7 day delay from initial cefadroxil administration to the onset of the reaction moderate risk for the development of drug reactions , while in veterinary medicine they are among the most commonly implicated drugs . for this reason , in the present case a score of + 3 was assigned ( table 1 ) . according to the literature , there are not many descriptions of sjs / ten in cats : caprine antiserum against felv , injected intraperitoneally and subcutaneously in a felv - positive patient in an attempt to treat felv - associated gingivitis was the first drug to be associated with feline ten . other cases implicated cephaloridine prescribed to treat pyelonephritis , ampicillin for a respiratory infection and hetacillin for an abscess . griseofulvin , penicillin , aurothioglucose and cefalexin have also been reported to cause ten in feline patients . a d - limonene - based insecticidal shampoo caused severe acute epidermal necrosis in a cat . regarding prechallenge , unknown previous exposure to this drug was scored 0 ( table 1 ) . rechallenge with the same drug provides the most definitive proof of drug causality ; however , this is generally not recommended . this cat could not be rechallenged because of the rapidly worsening lesions and extreme pain , resulting in the owner electing euthanasia . as far as the clinical features are concerned there is usually an acute onset of systemic signs , such as pyrexia , anorexia , lethargy and depression . this cat was pyrexic , dehydrated and tachycardic at the time of the clinical consultation . initial skin lesions of sjs / ten in dogs and cats are erythematous or purpuric , with macular or patchy eruptions , followed by blisters and skin detachment . the percentage body surface area ( bsa ) where the epidermis is detached or easily detachable is used to separate sjs ( < 10% ) and ten ( > 30% ) , both in human and veterinary medicine . however , lesions including epidermal detachment are progressive , and this cat had a skin involvement of > 30% at the worst stage of the disease . in this cat , erosive / ulcerative lesions involved the ventral neck , abdomen , perivulvar region , periungual skin and medial aspect of the front and hindlimbs . the cat also presented exfoliative dermatitis on the dorsum and tail base and in both external ear canals . ocular and vulvar mucocutaneous junctions were affected , as well as periungual skin , while there was no mucosal involvement . this is in contrast with the literature , because it is stated that more than one mucosa is usually involved . in a recent case series of ten in three dogs , two cases had only one mucosa involved . again , lesions in these extremely severe reactions are progressive ; it can not be excluded that if this cat had survived longer , mucosal erosions would have been observed . the histological lesions in sjs and ten reflect the pathogenesis , namely lymphocyte - mediated epidermal cell death , which is more extensive than in em . the lesions progress from single cell necrosis to clusters of dying cells to full - thickness confluent necrosis . microscopic features of the different conditions often overlap ; histopathological examinations do not reliably differentiate em , sjs and ten . in this case , histopathological analysis revealed extensive epidermal ulceration , interface dermatitis with vacuolar degeneration , apoptosis at multiple epidermal levels and dermoepidermal detachment , consistent with a diagnosis of sjs / ten , while full - thickness confluent necrosis was not observed . multiple epidermal levels apoptosis was recently reported as the most common pattern of ten in dogs . regarding prognosis , a prognosis score ( scorten , score for ten ) has been constructed , considering age , concurrent diseases , serum urea , bicarbonate and glucose levels , tachycardia and the percentage of bsa involved . optimal management is strongly required ; most patients need to be transferred in intensive care units or burns centres . identification and withdrawal of the candidate drug through careful evaluation of the history is mandatory . in veterinary medicine , . advanced supportive therapy , pain therapy , antibiotic and symptomatic therapy for cutaneous and mucosal ulcerations are imperative . our cat was hospitalised and treated with methadone hydrochloride , antibiotics and fluid therapy , but after 4 days the owner elected euthanasia owing to the cat s rapidly worsening conditions . we report cefadroxil as a very probable cause of sjs / ten in a cat according to the alden , applied for the first time in a feline patient . detailed descriptions of sjs / ten cases in cats are lacking in literature , and a rapid diagnosis and dedicated supportive therapy is mandatory to improve the prognosis .
case summarya 5-year - old , spayed female , indoor - only domestic shorthair cat was referred with an acute history of multifocal cutaneous and mucocutaneous erosive - ulcerative lesions and skin detachment . 
 the lesions occurred on the seventh day of therapy with cefadroxil . 
 erosive - ulcerative and occasionally crusted lesions were apparent on the medial and lateral canthus of both eyes , ventral neck , abdomen , perivulvar region , periungual skin and medial aspect of the front and hindlimbs . 
 diffuse and severe exfoliation was present on the dorsum and tail base and in both external ear canals . 
 the cat was also dehydrated , tachycardic and febrile . 
 histopathological examination revealed extensive epidermal ulceration , interface dermatitis with vacuolar degeneration , apoptosis at multiple epidermal levels and basal , suprabasal and spinous dermoepidermal detachment . 
 the histopathological diagnosis was consistent with stevens  johnson syndrome / toxic epidermal necrolysis ( sjs / ten ) . 
 the recently reported algorithm of drug causality in epidermal necrolysis ( alden ) , currently used in human medicine , was applied and a score of + 6 was calculated ; this supported the view that sjs / ten in this cat was very likely to be associated with cefadroxil administration.relevance and novel informationthis clinical communication reports cefadroxil as a very probable cause of sjs / ten in a cat ; the alden was applied in this case and supported diagnosis .