Diagnosing the Treatment

The differential diagnosis remains broad. An underlying malignancy would explain the chronic progressive course, and superimposed hypercalcemia would explain the acute symptoms of polyuria, tremor, and memory changes. Endocrinopathies including hyperthyroidism or adrenal insufficiency are other possibilities. A chronic progressive infection, such as tuberculosis, is possible, although no epidemiologic factors that increase his risk for this disease are present.

The patient had serum calcium of 14.5 mg/dL, ionized calcium of 3.46 mEq/L, albumin of 3.6 g/dL, BUN of 62 mg/dL, and creatinine of 3.9 mg/dL (all values were normal 3 months prior). His electrolytes and liver function were otherwise normal. Moreover, he had hemoglobin level of 10.5 mg/dL, white blood cell count of 4.8 × 10⁹cells/L, and platelet count of 203 × 10⁹ cells/L.

Until this point, only nonspecific findings were identified, leading to a broad differential diagnosis with little specificity. However, laboratory examinations confirm the suspected diagnosis of hypercalcemia, provide an opportunity to explain the patient’s symptoms, and offer a “lens” to narrow the differential diagnosis and guide the diagnostic evaluation. Hypercalcemia is most commonly secondary to primary hyperparathyroidism or malignancy. Primary hyperparathyroidism is unlikely in this patient given the relatively acute onset of symptoms. The degree of hypercalcemia is also atypical for primary hyperparathyroidism because it rarely exceeds 13 mg/dL, although the use of concurrent vitamin D and calcium supplementation could explain the high calcium level. Malignancy seems more likely given the degree of hypercalcemia in the setting of weight loss, tobacco use, and history of malignancy. Malignancy may cause hypercalcemia through multiple disparate mechanisms, including development of osteolytic bone metastases, elaboration of parathyroid hormone-related Peptide (PTHrP), increased production of 1,25-dihydroxyvitamin D, or, very rarely, ectopic production of parathyroid hormone (PTH). However, none of these mechanisms are particularly common in bladder or prostate cancer, which are the known malignancies in the patient. Other less likely and less common causes of hypercalcemia are also possible given the clinical clues, including vitamin D toxicity and milk alkali syndrome (vitamin D and calcium carbonate supplementation), multiple endocrine neoplasia (a sister with “throat cancer”), and granulomatous disease (weight loss). At this point, further laboratory evaluations would be helpful, specifically determination of PTH and PTHrP levels and serum and urine protein electrophoresis.

With respect to the patient’s past medical history, his Gleason 3 + 3 prostate cancer was diagnosed 12 years prior to admission and treated with external beam radiation therapy and brachytherapy. His bladder cancer was diagnosed 3 years before admission and treated with tumor resection followed by 2 rounds of intravesical BCG (iBCG), 1 round of mitomycin C, and 2 additional rounds of iBCG over the course of treatment spanning 2 years and 6 months. The treatment was complicated by urethral strictures requiring dilation, ureteral outlet obstruction requiring left ureteral stent placement, and multiple urinary tract infections.

The patient’s last round of iBCG was delivered 6 months prior to his current presentation. The patient’s hospital admission 4 months earlier for severe sepsis was presumed secondary to a urologic source considering that significant pyuria was noted on urinalysis and he was treated with meropenem, although bacterial cultures of blood and urine were sterile. From the time of discharge until his current presentation, he experienced progressive weakness and an approximately 50 lb weight loss.

The prior cancers and associated treatments of the patient may be involved in his current presentation. The simplest explanation would be metastatic disease with resultant hypercalcemia, which is atypical of either prostate or bladder cancer. The history of genitourinary surgery could predispose the patient to a chronic infection of the urinary tract with indolent organisms, such as a fungus, especially given the prior sepsis without clear etiology. However, the history would not explain the presence of hypercalcemia. Tuberculosis must thus be considered given the weight loss, hypercalcemia, and “sterile pyuria” of the patient. A more intriguing possibility is whether or not the patient’s constellation of signs and symptoms might be a late effect of iBCG. Intravesical BCG for treatment of localized bladder cancer is occasionally associated with complications. BCG is a modified live form of Mycobacterium bovis which invokes an intense inflammatory reaction when instilled into the bladder. These complications include disseminated infection and local complications, such as genitourinary infections. BCG infection might also explain the severe sepsis of unclear etiology that the patient had experienced 4 months earlier. Most interestingly, hypercalcemia has been described in the setting of BCG infection. Diagnosis of disseminated BCG is best made via culture or polymerase chain reaction testing for M. bovis at potential sites of involvement, including the blood. Nevertheless, a common presentation of a common disorder is still most likely. If his current presentation is distilled down to a chronic presentation of weakness, weight loss, and hypercalcemia in the setting of known malignancy, then the underlying malignancy seems to offer the most unifying explanation. Given that neither of his known cancers are commonly associated with hypercalcemia, the possibility that he has developed a third malignancy must also be considered.

In the hospital, the patient received intravenous normal saline, furosemide, and pamidronate. Evaluation for hypercalcemia revealed appropriately suppressed PTH (8 mg/dL), and normal levels of PTHrP (<.74 pmol/L), prostate specific antigen (<.01 ng/mL), and morning cortisol (16.7 mcg/dL). Serum and urine electrophoresis did not show evidence for monoclonal gammopathy, and the 25-hydroxy vitamin D level (39.5 ng/mL) was within the normal limits (normal range 20.1-50.0 ng/mL). The patient had elevated levels of 1,25-dihydroxy vitamin D (122 ng/mL, normal range 19.9–79.3 pg/mL), lactate dehydrogenase (196 units/L, normal 50–150 units/L), and angiotensin-converting enzyme (153 units/L, normal 14–82 units/L).

The suppressed PTH level makes primary hyperparathyroidism unlikely, the low PTHrP level decreases the probability of a paraneoplastic process, and the normal protein electrophoresis makes multiple myeloma unlikely. The presence of a significantly elevated 1,25-dihydroxy vitamin D level with a normal 25-hydroxy vitamin D level indicates extrarenal conversion of 25-hydroxy vitamin D by 1-hydroxylase as the etiology of hypercalcemia. Increased activity of 1-hydroxylase is the most consistent with granulomatous diseases, including sarcoidosis, and, with the exception of lymphoma, would not be expected in hypercalcemia malignancy. This mechanism is also associated with tuberculosis, disseminated fungal infections, such as coccidioidomycosis and histoplasmosis, and as a late effect of BCG treatment, regardless of whether disseminated infection or granulomatous immune response. Elevated lactate dehydrogenase and angiotensin-converting enzyme levels may also be noted in many of these disorders.