Two cases of severe vitamin D3 intoxication treated with therapeutic plasma exchange and high cut-off hemodialysis

We report on a 53-year-old female patient and a 33-year-old male patient presenting with life-threatening hypercalcemic crisis caused by self-induced vitamin-D intoxication. Both patients took high doses of vitamin D3 supplements, cumulatively up to 2,500,000–10,000,000 I.U. over several months. Accordingly, serum 25-OH-vitamin D concentrations were increased to 663 and 1289 nmol/L (reference 50–175 nmol/L), respectively. As forced diuresis and bisphosphonates failed to correct recurrent hypercalcemia, we hypothesized that add-on extracorporeal treatments might help overcome the refractory situation. Considering the binding of vitamin D3 metabolites to vitamin D-binding protein (VDBP, 59 kDa), we started extracorporeal treatments involving total plasma exchange with replacement by human albumin and by fresh frozen plasma, online hemodiafiltration and high cut-off hemodialysis. We found that in the former case, total plasma exchange with albumin and fresh frozen plasma and high cut-off hemodialysis lowered both 25-OH-vitamin D3 and 1,25-OH-vitamin D3, whereas in the latter case total plasma exchange with albumin was found to more effectively remove vitamin D metabolites compared to high cut-off hemodialysis. In contrast, the amount of total plasma calcium removed by high cut-off hemodialysis was higher compared to total plasma exchange with albumin. During follow up, patients 1 and 2 achieved almost normal total plasma calcium and vitamin D concentrations after 355 and 109 days, respectively. These two cases suggest that extracorporeal treatments with high cut-off hemodialysis and total plasma exchange with albumin may be considered as add-on treatment in refractory cases of vitamin D3-induced hypercalcemia to lower plasma 25-OH-vitamin D3 concentrations.


Introduction
In humans, plasma calcium concentration is maintained within a very narrow range. Intestinal calcium absorption is the limiting step of calcium balance and is governed by active 1,25-OH-vitamin D 3 , which is produced by the proximal tubule after 1α-hydroxylation of 25-OH-vitamin D 3 . Typically, the plasma concentration of 25-OH-vitamin D 3 exceeds that of 1,25-OH-vitamin D 3 by a factor of 1000 so that 25-OH-vitamin D 3 can be considered as a large reservoir. In plasma, 25-OH-vitamin D 3 and 1,25-OH-vitamin D 3 circulate bound to the vitamin D-binding-protein (VDBP), which has a molecular weight of 52-59 kDa [1].
Vitamin D can be supplemented by oral intake of cholecalciferol or vitamin D 3 , which is converted to 25-OH-vitamin D 3 by the liver. Vitamin D intoxication and resulting hypercalcemia are rare in clinical practice [2]. Due to its high lipophilicity, 25-OH-vitamin D 3 stores are eliminated slowly and symptom control may take several months [3]. In theory, extracorporeal treatment procedures can be considered for severe cases of vitamin D 3 intoxication [4,5]. However, due to its high lipophilicity and protein binding, removal of vitamin D 3 metabolites using conventional hemodialysis is not feasible. In neurologic patients, therapeutic/total plasma exchange (TPE) has been shown to remove vitamin D 3 metabolites [4]. Given the elimination of proteins up to 60 kDa, high cut-off hemodialysis might effectively remove vitamin D 3 metabolites bound to VDBP from the bloodstream [6]. To our knowledge, there are no reports of severe vitamin D 3 intoxication treated by extracorporeal removal of vitamin D 3 metabolites. Here, we suggest that extracorporeal treatments may be considered as add-on treatment in refractory cases of vitamin D 3 -induced hypercalcemia.

Methods
The 25-OH vitamin D concentrations in blood plasma, eluate and dialysate were measured by mass spectrometry (LC-MS/MS) using the Cascadion™ SM Clinical Analyzer (Thermo Fisher Scientific). For the determination of dialysate 25-OH vitamin D concentrations, samples were concentrated 40-fold via ultrafiltration using an Amicon ® Ultra-4 10 K centrifugal filter device (Merck, Germany). 1,25-OH-vitamin D3 concentration was measured using chemiluminescence immunoassay (IDS-ISYS, Immunodiagnostic System). Plasma creatinine was determined enzymatically and calcium concentration was determined using photometric endpoint determination (o-cresolphthalein complex method) on ADVIA Chemistry XPT system (Siemens Healthineers).

Patient information
A 53-year-old female was initially admitted to the hospital for treatment of relapsing progressive multiple sclerosis diagnosed 15 years earlier. She presented to our hospital with aggressive behavior, slow thinking, impaired cognition, and fatigue. In addition, she showed limited ability to walk and pain in the legs and left shoulder with radiation and weakness in the left arm. She had taken around 30,000 I.U./ days cholecalciferol (vitamin D 3 ) in the previous 16 weeks (total approximately 2,500,000 I.U.) in an attempt to positively impact the course of her multiple sclerosis and to compensate for vitamin D deficits, as widely communicated in the media.

Clinical findings
Physical examination showed normal and symmetrical reflexes, hyperactive biceps reflexes with an expanded reflex zone on both sides. There were no other previously unknown clinical findings attributable to hypercalcemia.

Therapeutic intervention
Upon hospital admission, the patient was treated with forced diuresis consisting of intravenous fluid replacement (2.5-5.6 L/days), torasemide (10-30 mg/days) and spironolactone (50 mg/days), which resulted in a lowering of the plasma calcium concentration to 3.1 mmol/L. As elevated concentrations of vitamin D 3 metabolites persisted and maintained the hypercalcemia, we decided to perform therapeutic plasma exchange with 5% human albumin (TPE-HA) as replacement fluid to remove circulating vitamin D 3 metabolites. After inserting a central venous dialysis catheter and exchanging approximately one plasma volume (2.5 L), plasma 25-OH-vitamin D 3 concentration dropped by 52% (to 302 nmol/L, Fig. 1B) and that of 1,25-OH-vitamin D3 by 14% (to 119 pmol/L, Fig. 1C). However, 25-OH-vitamin D 3 rebounded to 514 nmol/L. Due to low fibrinogen concentrations, we performed another total plasma exchange with 10 units (approximately 3.11 L) of fresh frozen plasma (TPE-FFP) as replacement, which lowered 25-OH-vitamin D3 by 52%, but not that of 1,25-OH-vitamin D 3 (Fig. 1C). Repeating therapeutic plasma exchange with human albumin resulted in the reduction of both vitamin D metabolites. In the meantime, 2 mg of ibandronic acid was administered intravenously. To treat rebounding concentrations of 25-OHvitamin D 3 and calcium, we decided to perform HD with a high cut-off dialyzer (Table 1). Using high cut-off hemodialysis, 25-OH-vitamin D 3 and 1,25-OH-vitamin D 3 levels fell by 31 and 36%, respectively ( Fig. 1B/C). To lower the plasma calcium concentration, we decided to perform online hemodiafiltration (HDF) with a high flux dialyzer ( Table 1). As expected, no changes in 25-OH-vitamin D 3 and 1,25-OH-vitamin D 3 concentrations were achieved. Plasma calcium concentration finally normalized (Fig. 1A), allowing the patient to be discharged after 30 days of hospitalization. However, 25-OH-vitamin D 3 concentration remained elevated at 374 nmol/L.

Follow-up and outcomes
During follow-up, there was a subsequent increase in plasma 25-OH-vitamin D 3 and calcium concentrations in the patient. Upon relapse of hypercalcemia at 3.2 mmol/L, she was again hospitalized and underwent forced diuresis with torasemide and administration of another dose of ibandronic acid (2 mg) intravenously. This corrected the hypercalcemia and the patient was discharged on loop diuretics. Two months later, there was another relapse of hypercalcemia (3.1 mmol/L) in the setting of persistence of elevated plasma concentrations of 25-OH-vitamin D 3 (476 nmol/L). 24-h urine collection revealed increased calcium excretion which prompted us to reduce the patient's calcium intake through a low calcium diet. Using tap water with a commercial liquid filter system (Brita ® MAXTRA +), the calcium concentration decreased by 90% from 1.94 mmol/L to 0.2 mmol/L. After 9 months of follow-up, kidney function stabilized at an eGFR-CKD-EPI of 36 mL/min/1.73m 2 (plasma creatinine level of 141 µmol/L or 1.6 mg/dL), while the plasma calcium concentration and the vitamin D 3 metabolites were (almost) normalized (Fig. 1).

Patient information
A 33-year-old male initially visited his family doctor because of persistent nausea, vomiting, headache, stomach pain and drowsiness, as well as polyuria and polydipsia. Laboratory examination performed in a different hospital showed lifethreatening hypercalcemia, leading to emergency admission of the patient. He had taken up to 35,000 I.U./days of vitamin D3 over the previous 6-12 months (total approximately

Clinical findings
Elevated blood pressure up to 200 mmHg systolic was detected, while in all other organ systems there were no abnormal findings that could be attributed to hypercalcemia.

Diagnostic assessment
Hypercalcemia with total and ionized plasma calcium concentrations of 4.0 mmol/L and 2.19 mmol/L ( Fig. 2A),respectively, as well as an elevated plasma concentration of 25-OH-vitamin D3 of 1289 nmol/L (Fig. 2B) and normal concentrations of 1,25-OH-vitamin D3 of 178 pmol/L (Fig. 2C) were detected. An increased plasma creatinine concentration of 193 µmol/L or 2.2 mg/dL (reference < 97 µmol/L or < 1.1 mg/dL) indicated acute kidney injury (Fig. 2D). There was no evidence of a pre-renal or post-renal condition, malignancy or primary hyperparathyroidism. Figure 3 describes the removal of 25-vitamin-D, 1,25-vitamin D and calcium performing different methods like hemodialysis for example.

Therapeutic intervention
The patient was transferred to the intensive care unit due to the life-threatening situation and, after inserting a central venous catheter, was immediately treated with sustained low efficiency dialysis (one session) and intermittent hemodialysis (three sessions) to correct hypercalcemia ( Fig. 2A). In addition, torasemide (5-20 mg/days), intravenous fluids (3.0-6.7 L/days) and 3 mg ibandronic acid were administered. Based on our prior experience with patient 1, we focused treatment on total plasma exchange with humanalbuimin and high cut-off hemodialysis to eliminate vitamin D 3 metabolites. As described above, we performed four sessions of therapeutic plasma exchange with human albumin with an exchange volume of 2.5-3.5 L corresponding to 0.61-0.85 times the plasma volume, and three 6 h sessions To investigate the efficacy of both treatments, we analyzed the plasma eluate of plasma exchange with human albumin and spent dialysate from high cut-off hemodialysis. We found that, depending on the initial value, the amount removed was between 1046 and 3168 nmol 25-OH-vitamin D 3 for plasma exchange with human albumin (four measurements) and 660 nmol (one measurement) for high cut-off hemodialysis. Regarding 1,25-OH-vitamin D 3 , total plasma exchange with human albumin removed 162-510 pmol, and high cut-off hemodialysis removed 134 pmol. The total removed amount of calcium in high cut-off hemodialysis was 36 mmol and up to 6-times higher compared to total plasma exchange with human albumin (max. 6-9 mmol). The patient was discharged with normal plasma calcium and 1,25-OH-vitamin-D 3 concentrations, while plasma 25-OH-vitamin-D 3 concentration was still elevated (383 nmol/L; Fig. 2B).