Heterotopic ossification in the setting of neuromuscular blockade

Heterotopic ossification (HO) is a disorder characterized by the formation of new bone in tissue that does not ossify under normal conditions. We report a series of 6 cases in which HO occurred in the setting of adult respiratory distress syndrome (ARDS). We wished to show that HO can occur after neuromuscular blockade and that these cases might provide additional evidence that HO is influenced by neural mechanisms.

Cases of HO were selected from the consultation services at the Massachusetts General Hospital and the Brigham and Women's Hospital. Affected patients all had ARDS and had been treated with a neuromuscular blocking agent. Patients with a history of stroke, burn, head trauma, spinal cord injury, or joint replacement were excluded from this study.

Heterotopic bone appeared around large joints in a pattern identical to that seen in patients with paralysis, traumatic brain injury, severe burns, or trauma. New bone formation was self-limited over a period of 1-2 years. Alkaline phosphatase and technetium bone scan were sensitive ways of detecting early disease and monitoring disease activity. Medical therapies had limited benefit. Surgical excision of mature new bone appeared to be the only definitive therapy.

Neuromuscular blockade in the setting of ARDS appears to be an important risk factor for the development of HO. The similarity of these cases of HO occurring in patients with brain or spinal cord injury raises the possibility that neural mechanisms may be important in the pathogenesis of this disease. Whether the type of neuromuscular blocking agent and the duration of use are important determinants of disease severity remains to be determined.