Aetiology of spinal deformities in neurofibromatosis 1: new hypotheses

Grade V Thoracic Spondylolisthesis in Neurofibromatosis Type 1: Case Report and Literature Review

BACKGROUND

Grade V thoracic spondylolisthesis secondary to neurofibromatosis type 1 (NF-1), especially combined with vertebral fusion, is rare. We reported a case of a 26-year-old female diagnosed with grade V T2spondylolisthesis and T2-T5 autofusion secondary to NF-1, which caused severe kyphotic deformity and neurologic deficits, and she was treated with posterior decompression, internal fixation, and fusion.

CASE DESCRIPTION

The right-handed patient admitted to the clinic due to weakness of her legs. An eye examination documented a sign of Lisch nodules in the iris. Café-au-lait macules, dermal neurofibroma of multiple forms, and rubbery bumps of varying sizes could be observed on her skin. Paresis with muscle strength of 2/5 in both lower extremities with increased muscle tone and decreased muscle mass could be observed. Radiographic results indicated grade V thoracic spondylolisthesis with vertebral fusion from T2-T5 level. To alleviate neurologic dysfunction, posterior decompression, internal fixation, and fusion were performed. She reported marked improvement in lower limb motor and sensory functions during the follow-up, and her muscle strength recovered to 5/5.

CONCLUSIONS

Grade V thoracic spondylolisthesis combined with vertebral fusion on T2-T5 level in NF-1 is rare. Early surgical intervention of posterior spinal decompression with internal fixation and fusion yielded satisfactory clinical outcomes.

Neurofibromatosis type 1-associated multiple rectal neuroendocrine tumors: A case report and review of the literature

Neurofibromatosis type 1 (NF-1) is commonly associated with benign or malignant tumors in both the central and peripheral nervous systems. However, rare cases of NF-1-associated multiple rectal neuroendocrine tumors have been reported. This report describes a case of a 39 year old female with NF-1 and intermittent hematochezia as a primary symptom. Physical examination showed multiple subcutaneous nodules and café au lait spots with obvious scoliosis of the back. Imaging examinations and colonoscopy found malformation of the left external iliac vein and multiple gray-yellow nodules with varying sizes and shapes in the rectal submucosal layer. Histological and immunohistochemical results suggested multiple rectal neuroendocrine tumors, a rare disease with few appreciable symptoms and a particularly poor prognosis. The patient with NF-1 presented here had not only multiple rectal neuroendocrine neoplasms but also vascular malformations, scoliosis and other multiple system lesions. This case therefore contributes to improving clinical understanding, diagnosis and treatment of related complications for patients with NF-1 who present with associated medical conditions.

Orthopaedic manifestations of neurofibromatosis type 1

Neurofibromatosis type 1 (NF-1) is an autosomal dominant disease that affects 1 in 3,000 persons worldwide. Café-au-lait macules and peripheral nerve sheath tumors (ie, neurofibromas) are the most commonly recognized manifestations of NF-1. However, NF-1 affects multiple organ systems, and a multidisciplinary approach to treatment is required. Management of the orthopaedic manifestations of NF-1 is often difficult. The most complex manifestations are scoliosis (dystrophic and nondystrophic), congenital pseudarthrosis of the tibia, and problems related to soft-tissue tumors. Metabolic bone disease is common; many patients are frankly osteopenic, which further complicates treatment. Dystrophic scoliosis, which may be caused by either bony dysplasia or intraspinal pathology, is characterized by early presentation and rapid progression. Pseudarthrosis is common even after instrumented fusion. Nondystrophic scoliosis tends to behave like adolescent idiopathic scoliosis, although it may present earlier and is associated with a higher rate of pseudarthrosis. Congenital pseudarthrosis of the tibia is a long-bone dysplasia that afflicts patients with NF-1. Management of this osseous deformity is challenging. Failure to achieve union and refracture are common.

Recent insights into bone development, homeostasis, and repair in type 1 neurofibromatosis (NF1)

Neurofibromatosis type 1 (NF1) is one of the most common single gene syndromes and is typified by a range of characteristic but variably penetrant manifestations. The orthopaedic manifestations of congenital pseudarthrosis of the tibia (CPT) and scoliosis, along with other skeletal defects including sphenoid wing dysplasia, rib penciling, and gracile bones have been classically associated with NF1. Added to this, several recent studies have reported a high prevalence of osteoporosis or osteopenia in NF1 cohorts. Clues to the underlying molecular and cellular deficiencies that cause these bony defects can be gleaned from genetically modified mouse models of Nf1 gene deficiency. These studies suggest that a variety of different cell lineages may be adversely affected by Nf1 haploinsufficiency or by double inactivation of the Nf1 gene. Osteoblasts, osteoclasts, chondrocytes, fibroblasts, and vascular endothelial cells all express the Nf1 gene product, neurofibromin, and may be functionally compromised when levels are decreased or absent. This paper reviews the current literature on NF1 bone development, homeostatic regulation, and repair, and highlights some emerging themes that may have relevance for managing orthopaedic disorders that can arise in individuals with NF1.

Neuroimaging findings in neurofibromatosis type 1 and 2

Neuroimaging, particularly MR imaging, plays an important role in the diagnosis and management of the patient with neurofibromatosis type 1 and 2. These phakomatoses are complex disorders affecting multiple cell types and multiple systems of the body with a wide range of expression. This article summarizes the neuroradiologic central nervous system findings in these neurocutaneous disorders.

Skeletal disorders associated with skin pigmentation: a role of melatonin?

Although frequently encountered, no available consensus about the association between skeletal abnormalities and skin pigmentation. Several syndromes are characterized by the presence of skin pigmentation in association with skeletal disorders like neurofibroamtosis 1, McCune-Albright Syndrome, Jaffe-Campanacci Syndrome and Jaffe-Lichtenstein Syndrome. Even in the absence of these syndromes, skeletal abnormalities were detected in all radiologically examined patients having patterned skin pigmentation. Although skin pigmentation is controlled by several factors, melatonin is the most reliable factor to have relation to development of skeletal abnormalities. Recent research works support that melatonin might play a role in bone development and several hypotheses link melatonin with some bone diseases associated with skin pigmentation. It seems that melatonin deficiency is a probable operating co-factor in a lot of clinical situations characterized by skin pigmentation and skeletal disorders. This would explain some of the un-explained observations related to these syndromes and research works along these lines might lead to the development of efficient treatment for these diseases.

Bone development in neurofibromatosis 1

Bony abnormalities are common findings in cases of neurofibromatosis 1. We might hypothesize that neurofibromin, the protein encoded by the neurofibromatosis 1 gene, plays important roles in bone development. Loss of function of oligodendrocyte-myelin glycoprotein gene and increased activity of ras p21 might increase the level of c-fos proto-oncogene in bones with formation of fibrous dysplasia-like tissue. Also, increased ras p21 might disturb collagen I synthesis by osteoblasts. Moreover, increased ras activity might increase the mitogenic signals to the nucleus through mitogen-activated protein kinase (MAPK) and disturb the level of the transcription factor core-binding factor alpha(1) (Cbfa1). Abnormal fibrous tissue and neurofibromas formed at the site of pseudarthrosis might represent abnormal response of periosteal fibroblasts for injury, an effect simulating the response of skin fibroblasts in neurofibromatosis 1 to injury.

Melatonin deficiency and fibrous dysplasia: might a relation exist?

Fibrous dysplasia of bone might be monostotic, polystotic, or occurs as a part of McCune-Albright syndrome and Jaffe-Lichtenstein syndrome. Activating mutations of GNAS1 gene was identified in patients with fibrous dysplasia. However, fibrous dysplasia might occur in the absence of these mutations and fibrous dysplastic tissue was produced in vitro by the effects of excess exogenous cAMP on human osteogenic cells. It was proved that the fibrous dysplastic tissue is deficient in bone sialoprotein. Melatonin deficiency might be hypothesized in syndromes associated with fibrous dysplasia or formation of fibrous dysplasia-like tissue. The receptor RZR/ROR is the nuclear receptor of melatonin and the human bone sialoprotein gene contains a RZR/ROR response element. It was supposed that binding of melatonin to its membrane receptors results in changes in the levels of activity of nuclear cAMP that lead to alteration of expression of bone sialoprotein. Also, melatonin deficiency might increase cAMP in bone through its effect on prostaglandins of the E group. Further, melatonin deficiency might explain precocious puberty in cases of McCune-Albright syndrome. We might hypothesize that melatonin deficiency might play a role in development of fibrous dysplasia in some cases.

Hypophosphatemic osteomalacia in neurofibromatosis 1: hypotheses for pathogenesis and higher incidence of spinal deformity

Osteomalacia is rarely encountered in association with neurofibromatosis 1, characterized by phosphate loss in the urine and its pathogenesis is still unknown. Incidence of spinal deformities in cases of neurofibromatosis 1 associated with osteomalacia seems to be high. Spinal deformities are unlikely to be due to osteomalacia itself. Melatonin deficiency was proposed to be present in cases of neurofibromatosis 1 and to be an operating factor in progression of spinal deformities. We might hypothesize that putative melatonin deficiency in cases of neurofibromatosis 1 might play a role in the pathogenesis of hyperphosphaturea by decreasing sodium-phosphate cotransport, increasing the level of cAMP, the un-antagonized effect of dopamine on phosphate reabsorption and increasing glucocorticoid levels. Parathyroid overactivity that may occur secondary to osteomalacia might have synergistic effects with dopamine and further exaggerate phosphate loss in urine. On the other hand, excess corticosteroid secretion would decrease nocturnal melatonin level. Moreover, in the presence of hypophosphatemia, hypercortisolism might further inhibit melatonin secretion that might lead to progression of spinal deformities in these cases.

The role of neurofibromin and melatonin in pathogenesis of pseudarthrosis after spinal fusion for neurofibromatous scoliosis

We might hypothesize that the high rate of pseudarthrosis after spinal fusion for neurofibromatous scoliosis is related to two factors: the absence of neurofibromin and melatonin deficiency. Loss of the up-regulation of neurofibromin during the healing process might abolish the bone-forming effects mediated through platelet-derived growth factor (PDGF) and transforming growth factor (TGF) beta1. The absence of neurofibromin might cause an increase in the Ras activity that increases the mitogen-activated protein kinase (MAPK) with resultant disturbance of the regulatory mechanism of core binding transcription factor (Cbfa 1) and increase of osteocalcin. These effects might inhibit bone formation. Melatonin deficiency might cause defective bone formation and favour excess fibrous tissue formation.

The association of neurofibromatosis 1 and spinal deformity with primary hyperparathyroidism and osteomalacia: might melatonin have a role?

A 35-year-old woman with neurofibromatosis 1 and thoracic kyphoscoliosis had incomplete paraplegia. She had a history of hyperparathyroidism due to a parathyroid adenoma which had been excised 4 years previously. Plain radiographs of the spine revealed kyphoscoliosis from the third to sixth thoracic vertebrae. Kyphosis and scoliosis angles were 86 degrees and 28 degrees, respectively. Radiographs of the skull and hands showed radiological changes suggestive of hyperparathyroidism. Laboratory tests showed low-normal serum calcium, hypophosphatemia, elevated serum alkaline phosphatase, and low serum 25-hydroxyvitamin D. Retrospective review of the patient's laboratory data showed that she had osteomalacia at the time of diagnosis of primary hyperparathyroidism. The patient had been treated by anterior and posterior decompression and fusion with posterior instrumentation through a single posterior approach. The postoperative kyphosis and scoliosis angles were 30 degrees and 12 degrees, respectively. Neurological recovery and spinal fusion had been achieved. Osteomalacia responded well to vitamin D therapy. This is the first case of coexisting neurofibromatosis 1, primary hyperparathyroidism due to parathyroid adenoma and osteomalacia to be reported in the literature. The osteomalacia in this patient could be related to primary hyperparathyroidism, and not to neurofibromatosis 1. A drop in melatonin level after parathyroidectomy may have been the cause of spinal curvature progression in this patient.