Exfoliative Dermatitis (red inflammed) involving >90% skin surface
inflammed, scaly, oedematous skin with systemic malaise/fever and LN
insidious onset unless drug induced
men>women, 40-60yrs

causes 
previous skin disease (60%) - psoriasis or eczema
lymphoma - esp cutaneous Tcell - Mycosis Fungoides (mushroom like fungal disease but actually a cutaneous Tcell lymphoma) and Sezary syndrome (?late stage Mycosis fungoides with lymphadenopathy) (leukaemia)
drugs (sulphonamides, gold, sulphonylureas, penicillin, allopurinal, captopril, cimetidine, carbamazepine)
idiopathic
rarer - pityriasis rubra pilaris, seborrhoaic and contact dermatitis, pemphigus foliaceous, Norwegian scabies and Netherton syndrome (neonates)
  
Mx
admit
treat cause if known
emollients / wet wraps to maintain hydration
topical steroids for inflammation
beware - fluid loss (cardiac failure, electrolyte imbalance, hypoalbuminaemia), infection, hypothermia
20-40% mortality

Erythrodermic psoriasis
    may result from progression of chronic disease to an exfoliative phase with plaques covering most of the body. Associated with mild systemic upset
    more serious form is an acute deterioration. This may be triggered by a variety of factors such as withdrawal of systemic steroids. Patients need to be admitted to hospital for management