Multiple Myeloma and Alkaline Phosphatase.

TO THE EDITOR

The article entitled “Bone-Specific Alkaline Phosphatase Levels among Patients with Multiple Myeloma Receiving Various Therapy Options”, written by Çetin et al. [1] and published in a recent issue of your journal, was quite interesting. Here we would like to emphasize some relevant points.

This study was not homogeneous. It is important that the initial value of total alkaline phosphatase (ALP) be measured. In addition, in that study, had serum intact parathyroid hormone level, vitamin D level, or bone turnover markers been available, they would have provided further biochemical correlates of skeletal metabolism.

Bone-specific ALP may increase in Paget’s disease, osteosarcoma, bone metastases of prostatic cancer (high/very high ALP values), other bone metastases, fractured bones, multiple myeloma (only when associated with fractures), osteomalacia, rickets, vitamin D deficiency (moderate rise), malignant tumors (ALP originating from tumors), renal disease (secondary hyperparathyroidism), and primary hypothyroidism [2,3].

Vitamin D deficiency is extremely common in multiple myeloma, with 40% of patients having vitamin D levels in the deficient range of levels less than 36 nmol/L, and it represents a surrogate for clinical multiple myeloma disease status [4].

Vitamin D deficiency can cause osteomalacia and those patients can develop generalized musculoskeletal pain, proximal muscle weakness, and increased risk of falls. This may not be clinically detectable but is nonetheless present and often unrecognized [5].

Conflict of Interest Statement

The authors of this paper have no conflict of interest, including specific financial interests, relationships, and/or affiliations relevant to the subject matter or materials included in this manuscript.

REPLY

At the beginning of the study we had planned to use some other parameters with a standard multiple myeloma work-up. We consulted with biostatisticians. As we compared a wide variety of patient groups in this analysis, according to the biostatisticians adding new parameters to our data would complicate the study. Therefore, we had to exclude some parameters.

We thank the reviewers for their valuable comments. We agree to plan further studies with new therapy options in small patient groups adding serum intact parathyroid hormone level, vitamin D level, and bone turnover.