Cystic back acne is one of the toughest places to treat acne and one of the most affected areas by taking a course of Accutane. I would have no concerns prescribing it based on what you have said, but a true evaluation must be conducted in person by a trained dermatologist. Accutane for body acne though is extremely effective.
"This answer has been solicited without seeing this patient and cannot be held as true medical advice, but only opinion. Seek in-person treatment with a trained medical professional for appropriate care."