Polycystic Bone Disease - An Overview

Introduction

Radiographic investigations effectively diagnose various pathological conditions related to the bone. It is very common for an isolated cyst-like lesion to occur in skeletal parts of the body due to multiple causes. Cyst-like lesions show a radiolucent appearance in the radiographic findings. In rare cases, multiple skeletal cysts are seen in conditions like bone tumors, bone dysplasias, and tumor-like conditions of the bone. A rare bone disorder with bony radiolucent cyst-like lesions was reported throughout the body. This condition was referred to as polycystic bone disease. This article will discuss polycystic bone disease, its clinical features, radiographic findings, and differential diagnosis.

What Is Polycystic Bone Disease?

The novel polycystic bone disease was first reported in the year 1999 by Micheal P. Whyte.

• Polycystic bone disease is a sporadic skeletal disorder with numerous small and large cyst-like lesions occurring throughout the skeletal system.

• The patients affected by these conditions are at high risk of frequent pathological bone fractures.

• The cyst-like lesions occur both in the axial and appendicular skeleton.

• The axial skeleton encompasses the bones along the body's central axis, including those in the head, neck, chest, and back. The appendicular skeleton refers to all other body bones that connect to the axial skeleton.

• This condition is believed to be a genetic condition with an inheritance pattern of autosomal dominance.

• Polycystic bone disease was reported in a family of a father, a daughter, and a son with the same clinical and radiology findings.

How Is Polycystic Bone Disease Inherited?

The exact underlying cause of this new skeletal condition is unknown. However, the male-to-male transmission of the condition seen in the studied case report is believed to be inherited in an autosomal dominant pattern. Generally, for a genetic condition to occur, two copies of the harmfully altered DNA (deoxyribonucleic acid) material are required to cause the disease. In genetic disorders with a dominant pattern, a single copy of the altered gene is enough to cause the condition.

Autosomal refers to the mutated or altered gene in the first 22 pairs of non-sex chromosomes, not in the X and Y chromosomes (sex chromosomes). The probability of passing down the mutated gene from the parents increases by 50 percent with each pregnancy in an autosomal dominant pattern.

What Are the Clinical Features of Polycystic Bone Disease?

The clinical features of the condition are based on the findings seen in the family case report. The common features noted in these patients are mentioned below.

• Frequent occurrences of pathological fractures are seen in the wrist, forearm, shinbone, collarbone, upper arm bone, and ribcage.

• Joint pain, especially in the elbows.

• Hypermobility of joints, especially in the small joints of the hands.

• Mild knock knee deformity (malalignment of the knee).

• Weakening of the bone.

What Are the Investigation Methods for Polycystic Bone Disease?

1. Bone X-ray: The common radiological findings of polycystic bone disease are below.

• Multiple one to two centimeters radiolucencies were noted in the collarbone, ribcage, and shoulder blade.

• Multiple cyst-like lesions with bone expansion and thinning of the outermost layer of bone (cortical bone).

• Expanded and irregular bone margins of the ribcage and multiple fractures are noted.

• Large and multiple cysts of more than five-centimeter diameter are noted on the iliac bone (upper part of the hip bone).

• Hypomineralization of the upper spine is seen.

2. Skeletal Scintigraphy: Bone scan, a specialized radiographic technique used in the evaluation and assessment of various bone disorders.

• Multiple areas of the appendicular skeleton were seen with skeletal abnormalities.

• More intense uptake (an indicator of an oddity) is noted in the radial bone, iliac bone, and ribcage.

3. Bone Densitometry Test: A test used to evaluate the mineral content and density of the bone.

4. Biochemical Tests: A series of tests measured to assess the blood and urine of the affected patients. Routine urine analysis, complete blood count, and serum electrolyte levels are unusual. Parameters of bone homeostasis (bone turnover to maintain the equilibrium) are unusual.

5. Bone Biopsy: This investigative procedure is performed to remove a sample of bone tissue to be assessed under the microscope. They are otherwise referred to as closed or needle bone biopsy and in some cases, they are performed in the guidance of an MRI (Magnetic Resonance Imaging) or CT (Computed Tomography) scan.

What Are the Differential Diagnosis of Polycystic Bone Disease?

Multiple bone radiolucencies occur in various diseases similar to polycystic bone disease.

• Polyostotic Fibrous Dysplasia: A condition with multiple bone defects where the bone tissues are replaced with fibrous tissue, resulting in weakened bone, bone deformities, and irregular bone growth. Multiple cyst-like lesions increasing in size, similar to polycystic bone disease, are noted. However, in radiological studies, Polyostotic fibrous dysplasia has a distinctive round glass appearance.

• Rothmund Thomson Syndrome: An autosomal recessive condition characterized by juvenile cataracts, dental abnormalities, and skin rashes that progresses to poikiloderma (a benign pigmented skin disorder), osteosarcoma, and sparse hair. The skeletal defects of this condition show bone cysts and osteoporosis.

• Osteoglophonic Dwarfism: A condition characterized by short stature and distorted facial features. The radiographic features of this condition show irregular radiolucencies of the epiphyses (part of the long bones) and metaphyses (neck portion of the long bones).

• Satoyoshi Syndrome: A multisystemic syndrome that causes recurrent muscle spasms and various skeletal deformities. The skeletal abnormalities of the condition cause multiple cystic lesions, fractures, and bone fragmentation. This condition is also referred to as the Komuragaeri disease. Individuals affected by this condition may also have hair loss in the body and head.

• Congenital Generalized Fibromatosis: It is a rare condition characterized by multiple fibroblastic tumors of the bone, skin, and muscles. The condition causes cystic lesions of the metaphyseal bone.

• Noonan-Like Multiple Giant Cell Lesion Syndrome: A rare condition characterized by short stature, developmental delay, webbed neck, and giant cell lesions of bone. The skeletal abnormalities of this condition cause cyst-like lesions of the small tubular bones.

Conclusion

Polycystic bone disease is a highly uncommon condition characterized by the presence of small and large cyst-like lesions with increasing sizes all over the skeletal bones of the body. The affected patients are more prone to frequent pathological fractures. Inheritance of this condition follows an autosomal dominant pattern. The studies show no specific medical treatment and the long-term outcomes of the disease are inconclusive.