Thanks for your post.
Your patient's situation is puzzling-- it is unusual to see patients who are otherwise stable experience such a large decrease in absolute CD4 cell counts.
First, I'd want to know if the patient was having an active infection; you mention previous treatment for TB and current treatment for MAC. Is the later an active process? Does she have MAC bacteremia? or, was this empirical treatment?
You also mention a left lower lobe pulmonary infiltrate- does this represent recurrent TB or other pneumonia? If so, the active infection could result in a perturbation in the CD4 counts that might not otherwise be representative of treatment failure.
Both issues point to the difficulty (and unreliability) of performing CD4 (or viral load) testing during concomitant infection or complication.
As a control, I alway look at the CD4 percentage-- it's not unusual to see absolute numbers drop (particulary during periods of leukopenia or lymphocytopenia) but see relative preservation of the CD%.
If leukopenia is present, this finding alone may explain the drop in CD4 absolute count; this could suggest multiple issues, but with the possibility of MAC, i'd be concerned about marrow infiltrative disease (from MAC) or toxicity from one of your patients many medications.
I hope this is a useful starting point, good luck with your patient. BY
