Question: Which diseases are involved in the severe cutaneous reactions (SCAR) spectrum?

Context:
Stevens-Johnson Syndrome (SJS) and toxic epidermal necrolysis (TEN) are diseases within the spectrum of severe cutaneous adverse reactions affecting skin and mucous membranes. 
Toxic epidermal necrolysis (TEN) and Stevens Johnson Syndrome (SJS) are severe adverse cutaneous drug reactions that predominantly involve the skin and mucous membranes.
Currently, TEN and SJS are considered to be two ends of a spectrum of severe epidermolytic adverse cutaneous drug reactions, differing only by their extent of skin detachment. 
Toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS) are considered part of a spectrum of adverse cutaneous drug reactions showing severe and extensive skin detachment.
Our aim was to study patch testing in severe cutaneous adverse drug reactions (ADRs) (Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), acute generalized exanthematous pustulosis (AGEP), and other cutaneous ADRs)
However, allopurinol is also one of the most common causes of severe cutaneous adverse reactions (SCARs), which include drug hypersensitivity syndrome, Stevens–Johnson syndrome, and toxic epidermal necrolysis.
Drug eruptions range from transient erythema to the life threatening severe cutaneous adverse reactions (SCAR) that encompass Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), acute generalized exanthematous pustulosis (AGEP) and drug reaction with eosinophilia and systemic symptoms complex (DRESS).To study the clinical and epidemiological aspects of cutaneous adverse drug reactions (CADR).Ethical clearance was obtained from the institutional ethics committee
Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug reaction with eosinophilia and systemic symptoms (DRESS) are severe cutaneous adverse reactions (SCAR) which are majorly caused by drugs
This study investigated the association between the HLA class I genotype and carbamazepine-induced severe cutaneous adverse reaction (SCAR) in Koreans.Twenty-four patients who had developed carbamazepine-induced SCAR (7 Stevens-Johnson syndrome (SJS), 17 drug hypersensitivity syndrome (HSS)), 50 carbamazepine-tolerant controls from the Korean Pharmacogenetic Adverse Drug Reaction Research Network and data of 485 Korean general population from a previously published study were recruited
Severe cutaneous adverse reactions (SCARs) include Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug reaction with eosinophilia and systemic symptoms (DRESS)
Severe Cutaneous Adverse Reaction (SCAR) represents the spectrum of adverse drug reactions from erythema multiforme, Stevens - Johnson syndrome (SJS) to Toxic Epidermal Necrolysis (TEN). 
Toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS) are uncommon but extremely serious and often life-threatening mucocutaneous reactions characterized by extensive epithelial sloughing and systemic symptoms. There is no effective evidence-based treatment for severe cutaneous adverse reactions (SCAR) to drugs and no consensus on how to treat these patients.
However, allopurinol is also one of the most common causes of severe cutaneous adverse reactions (SCARs), which include drug hypersensitivity syndrome, Stevens–Johnson syndrome, and toxic epidermal necrolysis. A variant allele of the human leukocyte antigen (HLA)-B, HLA-B*58:01, associates strongly with allopurinolinduced SCAR.
The skin is often involved in ADRs and although most cutaneous ADRs have a favorable course, they may present as severe adverse cutaneous drug reactions (SCARs), such as Stevens-Johnson syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms (also referred to as drug-induced hypersensitivity syndrome), and acute generalized exanthematous pustulosis.
By comparison, Stevens-Johnson syndrome (SJS) is a life-threatening severe cutaneous adverse reaction (SCAR), mainly caused by drugs.
The study sought to identify the magnitude and characteristic of severe cutaneous adverse reactions (SCAR's) like Steven-Johnson syndrome (SJS) and Toxic Epidermal Necrolysis (TEN).
Allopurinol, an antihyperuricaemic agent, is one of the common causes of life-threatening severe cutaneous adverse reactions (SCAR), including drug rash with eosinophilia and systemic symptoms (DRESS), Stevens-Johnson syndrome (SJS) and toxic epidermal necrosis (TEN).

Answer: The diseases that are involved in the severe cutaneous reactions (SCAR) spectrum are:
1) Stevens-Johnson syndrome (SJS)
2) Toxic epidermal necrolysis (TEN)
3) Acute generalized exanthematous pustulosis (AGEP).
Exact answer: Stevens-Johnson syndrome, SJS, Toxic epidermal necrolysis, TEN, Acute generalized exanthematous pustulosis, AGEP