An 80 year old woman with dementia is visited in her nursing home by her General Practitioner after staff are concerned that she is uncontrollably scratching herself. On examination she has numerous excoriated papules on her upper limbs and trunk. Her General Practitioner has previously prescribed oral antibiotics and a topical steroid, but this only produced a temporary improvement. Three other residents have developed a similar eruption. What is the most likely diagnosis?
1) Scabies
2) Contact dermatitis
3) Atopic dermatitis
4) Psoriasis