Although the differential diagnosis of altered mental status is quite extensive, a patient with multiple myeloma and altered mental status should prompt consideration of one important, albeit not too common, condition.....hyperviscosity syndrome.
Some important pearls:
This syndrome occurs when excessive amounts of protein (immunoglobulin) are secreted by myeloma (plasma) cells.
Excessive circulating protein leads to sludging and ischemia in lung and brain tissue, lesding to hypoxia and altered mental status, respectively.
You will only pick up this diagnosis by thinking about it, so multiple myeloma + altered mental status = hyperviscosity syndrome
Treatment is with IVF and plasmapheresis (heme onc consult)
And don't forget common stuff, like stroke, subdural hematomas, meningitis, etc.
