Orthopedic aspects of familial insensitivity to pain due to a novel nerve growth factor beta mutation.

BACKGROUND

Congenital insensitivity to pain is a rare hereditary sensory neuropathy.

PATIENTS

We present 6 patients from a family with a mutation in the nerve growth factor beta gene (NGFB).

RESULTS

3 patients were homozygous with a mutilating arthropathy starting early in life, and 3 patients were presumably heterozygous with a milder course starting in adulthood. All patients had normal mental abilities. In addition to absence of deep pain, the patients had impaired temperature sensation, but no autonomic deficiency. Sural nerve biopsies showed a moderate loss of A-delta fibres and a severe reduction in C fibers. Clinically, the disorder most often affected the lower extremities, with an insidious progressive joint swelling or a painless fracture, but the spine could also be involved with gross and unstable spondylolisthesis. Fracture healing was uneventful, but the arthropathy was progressive, eventually resulting in gross deformity and instability. When treating patients with congenital disorders such as this one, it is important to consider the slowly progressive nature of the disorder, and the orthopedic operations should therefore be planned from a long-term standpoint. Arthrodesis, limb lengthening and spinal decompression or fusion are the only elective procedures that seem reasonable. Fitting of orthosis for joint protection is also demanding. To delay the development of neuropathic arthropathy, patient education is essential but difficult in the very young.

INTERPRETATION

The different expression between homo- and heterozygous subjects and the central role of nerve growth factor make this disease an interesting model system for studies of disease mechanisms and the molecular background to pain.