Bone pain

Bone pain belongs to the class of deep somatic pain, often experienced as a dull pain that cannot be localized accurately by the patient. This is in contrast with the pain which is mediated by superficial receptors in, e.g., the skin. Bone pain can have several possible causes ranging from extensive physical stress to serious diseases such as cancer.

Bones contain nerves. The periosteal layer (an outer membrane) of bone tissue is highly pain-sensitive and an important source of pain in several disease conditions causing bone pain, like fractures, osteoarthritis, etc. However, in certain diseases, the endosteal and haversian nerve supply seems to play an important role, e.g. in osteomalacia, osteonecrosis, and other bone diseases. Thus, there are several types of bone pain, each with many potential sources or origins of cause.

Causes

A number of diseases can cause bone pain, including the following:

• Endocrine, such as hyperparathyroidism, osteoporosis, kidney failure.
• Gastrointestinal or systemic, such as celiac disease and non-celiac gluten sensitivity (both often occur without obvious digestive symptoms), inflammatory bowel disease (including Crohn's disease and ulcerative colitis).
• Hematologic, such as Cushing's syndrome, histiocytosis, multiple myeloma and sickle cell anaemia.
• Infectious, such as Lyme disease and osteomyelitis.
• Neurological, such as spinal cord injury and vertebral degeneration.
• Oncologic, such as bone metastasis, oncogenic osteomalacia and leukemia.
• Rheumatic, such as ankylosing spondylitis, rheumatoid arthritis, gout.
• Others, such as fractures, osteoarthritis, Paget's disease of bone (also termed osteitis deformans or just Paget's disease).

Causes in children

• Acute leukemia
• Acute rheumatic fever, a very dangerous disease that can cause permanent cardiac damage
• Untreated celiac disease, which can present without gastrointestinal symptoms
• Fibromyalgia, which affects people of all ages
• Growing pains
• Hypermobility syndrome can present with knee or ankle pain
• Lupus
• Henoch–Schönlein purpura
• Fibrous dysplasia of bone
• Infection
• Injury such as a fracture
• Inflammatory bowel disease
• Juvenile idiopathic arthritis
• Legg–Calvé–Perthes disease
• Lyme disease, which is transmitted by ticks and is characterized by debilitating polyarthritis, neurologic symptoms, and erythema migrans
• Lymphoma
• Osteomalacia/rickets in adolescents
• Osteopetrosis
• Osteosarcoma
• Rickets
• Septic arthritis, a severe infection of the joint that can lead to permanent joint damage
• Spondyloarthropathies
• Viral diseases, including the measles, influenza, mononucleosis, chickenpox, and mumps.

Common causes of bone and joint pain in adults, such as osteoarthritis and gouty arthritis are rare in children, as these diseases are a sequelae of chronic wear and tear for several years.

Cancer

Pain caused by bone cancer is among the worst forms of pain. Because of its severity and uniqueness compared to other forms of pain, it has been researched extensively. From studies of bone cancer in mouse femur models, it has been determined that bone cancer pain results from destruction of bone tissue. Chemical changes within the spinal cord as a result give further insight into the mechanism of bone pain.

Metastatic cancer cells often establish themselves in the skeleton. When the cancer cells have metastasized, the mechanical dynamics of the bone matrix become weaker as skeletal strength decreases. This leads to several complications throughout the body, including pain, thus decreasing the patient's quality of life.

Bone tumors are a conglomeration of cell types, including cancer and immune system cells. Often, tumor cells secrete growth factors that activate receptors close to primary afferent neurons. Activation of these neural receptors is a contributing factor to pain. Also, inflammatory lipids called prostaglandins, which are produced at high rates by cancer cells within tumors, activate nociceptors when they bind together.