Concomitant Primary Hyperparathyroidism in Patients with Multiple Myeloma: A Possible Link?

Hypophosphatemia in Patients With Multiple Myeloma

Hypophosphatemia is among the most common electrolyte abnormalities, especially among patients with underlying malignancies, and is frequently associated with adverse prognoses. Phosphorus levels are regulated through a number of mechanisms, including parathyroid hormone (PTH), fibroblast growth factor-23 (FGF-23), vitamin D, and other electrolyte levels themselves. Clinically, the findings are nonspecific, and the diagnosis is frequently delayed. This article is a narrative literature review. The PubMed database was searched for relevant articles pertaining to hypophosphatemia causes and consequences in patients suffering from multiple myeloma. We found a variety of causes of hypophosphatemia in patients with multiple myeloma. Tumor-induced osteopenia, although more common among patients with small squamous cell carcinomas, can occur with multiple myeloma as well. Additionally, both light chains themselves and medications can trigger Fanconi syndrome, which leads to phosphorus wasting by the kidney. Bisphosphonates, in addition to being a possible cause of Fanconi syndrome, lead to a decrease in calcium levels, which then stimulates parathyroid hormone (PTH) release, predisposing the patient to significant hypophosphatemia. Additionally, many of the more modern medications used to manage multiple myeloma have been associated with hypophosphatemia. A better understanding of those mechanisms may give clinicians a clearer idea of which patients may need more frequent screening as well as what the potential triggers in the individual patient may be.

Plasma Cell Dyscrasia: A Case Series of a Masquerader

Plasma cell dyscrasia is a result of an abnormal clonal proliferation of plasma cells. These cells arise from B cells in the bone marrow and produce immunoglobulins. Multiple myeloma is a type of plasma cell dyscrasia that commonly presents with symptoms secondary to hypercalcemia, hyperviscosity, renal failure, and bone pain. Here, we report three patients with unusual presentations of plasma cell dyscrasias.

Inactivation of parathyroid hormone: perspectives of drug discovery to combating hyperparathyroidism

Hormonal coordination is tightly regulated within the human body and thus regulates human physiology. The parathyroid hormone (PTH), a member of the endocrine system, regulates the calcium and phosphate level within the human body. Under non-physiological conditions, PTH levels get upregulated (hyperparathyroidism) or downregulated (hypoparathyroidism) due to external or internal factors. In the case of hyperparathyroidism, elevated PTH stimulates cellular receptors present in the bones, kidneys, and intestines to increase the blood calcium level, leading to calcium deposition. This eventually causes various symptoms including kidney stones. Currently, there is no known medication that directly targets PTH in order to suppress its function. Therefore, it is of great interest to find novel small molecules or any other means that can modulate PTH function. The molecular signaling of PTH starts by binding of its N-terminus to the G-protein coupled PTH1/2 receptor. Therefore, any intervention that affects the N-terminus of PTH could be a lead candidate for treating hyperparathyroidism. As a proof-of-concept, there are various possibilities to inhibit molecular PTH function by (i) a small molecule, (ii) N-terminal PTH phosphorylation, (iii) fibril formation and (iv) residue-specific mutations. These modifications put PTH into an inactive state, which will be discussed in detail in this review article. We anticipate that exploring small molecules or other means that affect the N-terminus of PTH could be lead candidates in combating hyperparathyroidism.