Infantile Cortical Hyperostosis

Etiology

Gensure et al. performed a genome-wide scan followed by fine mapping of individuals with the ICH's autosomal dominant form. Subsequently, genes were sequenced, and PCR amplification was performed. Gel electrophoresis confirmed that the affected individuals had a missense mutation in the COL1A1 gene.[3]

Epidemiology

ICH rarely occurs after the first year of age.[4] Radiographic findings include cortical thickening (hyperostosis) and subperiosteal new bone formation. There is a prenatal form of the disease called lethal prenatal cortical hyperostosis, which shows an autosomal recessive mode of inheritance and occurs before 35 weeks gestation. Polyhydramnios, angular deformities of the long bones, deformities of the ribs, prematurity, and lung disease are associated with this form. The infantile (classical) form that appears after 35 weeks of gestation is less severe and more common.[2] Ultrasound in utero can show changes such as bone curvature and cortex deformities consistent with ICH.[4]

Pathophysiology

ICH's familial form is autosomal dominant with variable penetrance and classically associated with a COL1A1 point gene mutation (3040C to T) on chromosome 17q21.[5] This missense mutation results in an arginine to cysteine substitution (R836C) in the triple helix of the alpha-1 chain of type 1 collagen. Type 1 collagen is essential for bone mineralization and makes up about 9% of the bone matrix. These fibers comprise one a2 and 2 a1 procollagen chains followed by cleavage of the N and C termini by proteinases. Collagens provide strength and interact with proteins to form the extracellular matrix necessary for cell function.[6]

The relation between this missense mutation and the skeletal findings of ICH is unknown. Still, proposed mechanisms include an inability of chromosome interactions with proteins (IL-2), defective cross-linking between the bone and abnormal collagen, and decreased thermal stability of collagen.[6] The average age of presentation of ICH's familial form is between 6 to 8 weeks, commonly involving the tibias. Twenty-four percent of infants present at birth with the familial form. ICH's sporadic form usually involves the mandible with an average age of onset between 9 and 11 weeks. Some sporadic cases result from prolonged administration of prostaglandins E1 and E2 in infants with cyanotic heart disease.[4]

COL1A1 and COL1A2 gene mutations cause subtypes of Ehlers-Danlos syndrome and osteogenesis imperfecta. Gly substitutions in the triple helix lead to defective type I collagen resulting in fractures and findings consistent with osteogenesis imperfecta types II-IV. Some individuals with ICH have features seen in Ehlers-Danlos, such as hyperextensible skin, joint hyperlaxity, and inguinal hernias.[6]

Histopathology

Histologic findings in the early stages of the disease are limited to the periosteum. The periosteum’s fibrous layer gradually breaks down and becomes associated with muscles, tendons, and fascia. Osteoid trabeculae enter the muscles, soft tissue, and connective tissue, forming new bone and resulting in increased diameter. Eventually, the periosteum reforms a fibrous layer over the new bone, and the extra bone is removed.[4]

History and Physical

ICH commonly presents with sudden soft tissue swelling of the jaw and face, fever, and irritability. Some cases first present with swelling of the extremities followed by swelling of the face days later. These swellings become hard, fixed to the bone, and red and painful.[1] Other clinical findings can include conjunctivitis, decreased movement of extremities, failure to thrive due to difficulty eating, and pallor.[1]

Evaluation

Laboratory findings can include increased erythrocyte sedimentation rate, C-reactive protein, alkaline phosphatase or immunoglobulin levels, and leukocytosis or thrombocytosis. There are cases of ICH where laboratory findings are all within normal limits.[5]

Genetic testing, if available, can confirm the presence of the missense mutation but the clinical course and radiographic findings should establish a clinical diagnosis. X-rays show gradual cortical thickening, periosteal bone formation around the diaphysis, and soft tissue swelling. Magnetic resonance imaging (MRI) is consistent with periosteal thickening, low-signal intensity in soft tissues on T1 sequences, and high-signal intensity on T2 sequences. Changes take 15 to 20 days to appear on x-rays, making diagnosing ICH in the early stages difficult. Abnormal MRI findings may sometimes present before abnormal x-ray films.[2][4]

Treatment / Management

Treatment includes observation and counseling. Acetaminophen and non-steroidal anti-inflammatory medications such as naproxen, ibuprofen, and indomethacin have been reported to help with symptoms. Corticosteroids can be used in severe cases. However, they have not been proven to prevent recurrences.[5](B3)

Differential Diagnosis

Differential diagnoses include child abuse, malignancy, hypervitaminosis A, hypoparathyroidism, parotitis, osteomyelitis, prostaglandin administration, scurvy, or other collagen synthesis defects.[7][2][8]

Prognosis

The time of resolution can vary between weeks to years. Throughout the disease, swelling can improve in one area and reappear in the same or different locations. ICH usually spontaneously resolves within 2 years of age. On average, resolution occurs within 6 to 9 months. Both clinical symptoms and labs generally normalize during this time. There have been rare cases of reoccurrence in adolescence and adulthood.[4]

Complications

ICH usually resolves with no major clinical sequelae. A few cases have complications, including pleuritis, thoracic scoliosis, and exophthalmos. Rarely, bone deformities may require surgical correction at a later age.[4]