- Calcium (i.e. hypercalcaemia)
- Renal failure (acute or chronic)
- Anaemia (multifactorial)
- Bone pain (from lytic lesions or pathological fractures)
- Infections (they're heavily predisposed, mostly from their immune paresis)
There are other possibilities for presenting symptoms (e.g. tinnitus or visual disturbances secondy to hyperviscosity syndrome), but the main ones are certainly covered by the mnemonic above. And besides, adding too many others on to "CRAB infections" would just make it even sillier.