Nephrology

PCP submission

85-year-old female with CKD 3, overactive bladder, lumbar stenosis with neurogenic claudication. Her GFR was above 60 until about a year ago when it started to hover in the low 50s. Recently when her sodium began to drop into the low 120s and below. No symptoms.  Diuretics were stopped with no effect.  Previously on furosemide 20 mg QD.  HCTZ did not help her swelling. Serum osmolality at 256 and urine osmolality at 352. Previous PTH normal.

Meds include atorvastatin 10 mg, baclofen 10 mg for muscle spasm, levothyroxine 100mcg, metoclopramide 5 mg to help GERD, olmesartan medocomil 40 mg, oxybutynin chloride ER 10 mg and sodium bicarb 650 mg. She is being evaluated for other possible malignancies with a new CXR, CT and other testing.

What management would you recommend?  Could this be SIADH? Any thoughts on preventing this presentation in CKD patients? 

Specialist response

If a patient like this presented to me, these would be my general thoughts: Thanks for sharing this case. I suggest the following- 

1. Hyponatremia with low serum osmolarity confirms this is hypotonic hyponatremia and not pseudohyponatremia that sometimes can be seen with conditions like myeloma or hypertriglyceridemia. 
2. Urine osm higher than serum osm indicates increased ADH activity. question is whether its appropriate or inappropriate. 
3. Check orthostats, BNP, and echo, urine protein:creatine ratio and LFTS (if not recently checked). If this work up is abnormal then likely cause of hyponatremia will be effective volume depletion (either from volume depletion which may show orthostasis, heart failure may show abnormal BNP or echo, nephrotic syndrome which wil show proteinuria and cirrhosis which may show abnormal LFTs). Treatment will then depend on the underlying cause of SIADH. 
4. If above work up negative then very likely this is SIADH. In this case, check TSH, confirm not taking NSAIDS (NSAIDS block ADH inhibitory prostaglandins), consider stopping olmesartan as rare cases linked to this. Agree with malignancy work up as outlined consider kidney mass prior. 
5. If diagnosis is SIADH and no cause is found then in addition to fluid restriction, consider treating with urena 30 grams daily (link) 
6. It’s difficult to generalize hyponatremia etiologies to a population so best to approach each individually but polydipsia (urine osm will be lower than serum osm) and SIADH are common causes in this age group.