I would not delay treatment with ATG if they think your son's disease is immune-mediated, regardless of the label. One of the predictors for a response to ATG is whether it was given within 3-4 weeks of diagnosis. My treatment was also delayed an extra month while awaiting results from yet another inconclusive BMB. It is so frustrating!
Differentiating between AA and MDS in a hypocellular marrow with no chromosonal abnormalities is very difficult. It's hard to estimate dysplasia when there aren't a lot of cells to begin with. Also, a person's marrow can be patchy. For me, some of my BMB's were very hypocellular while others were mildly hypercellular. All of this confuses the diagnosis and ultimately delays the treatment. Meanwhile, the disease is progressing.
Some of my doctors told me that dysplasia meant that I did not have AA. Other's told me that if the dysplasia was not signficant, than it was still likely AA. If the disease is immune-mediated, does the label really matter?
I hope you reach resolution soon. I wish you both the best!
53 yo female, dx 9/08, AA/hypo-MDS, subclinical PNH, ATG/CsA 12/08, partial response. small trisomy 6 clone, low-dose cyclosporine dependent