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Updated: Mar 13 2023

Neurofibromatosis

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https://upload.orthobullets.com/topic/4054/images/hemihypertrophy - courtesy of Miller_moved.jpg
https://upload.orthobullets.com/topic/4054/images/Cafe au lait - colorado_moved.jpg
https://upload.orthobullets.com/topic/4054/images/scoliosis - courtesy of Miller_moved.jpg
https://upload.orthobullets.com/topic/4054/images/pseudoarthrosis - courtesy of Miller_moved.jpg
  • summary
    • Neurofibromatosis is an autosomal dominant disorder caused by a mutation in the NF1 gene that codes for the neurofibromin protein that typically presents with skin lesions, lower and upper extremity deformities, and spinal involvement. 
    • Diagnosis is made with the NIH Consensus Development Conference Statement criteria with the presence of a combination of cafe-au-lait spots, neurofibromas, freckling in axillary/inguinal region, optic glioma, lisch nodules, and the presence of a 1st degree relative with NF-1.
    • Treatment depends on presence and severity of forearm, lower extremity or spinal deformity.  
  • Epidemiology
    • Incidence
      • 1:3,000 births for NF1
    • Anatomic location
      • extremity deformities
        • congenital anterolateral bowing and pseudoarthrosis of tibia/ fibula and forearm
      • spine involvement
        • scoliosis & kyphosis
        • atlantoaxial instability
  • Etiology
    • Genetics
      • autosomal dominant (AD)
      • mutation in NF1 gene on chromosome 17q11.2
        • codes for neurofibromin protein
          • negatively regulates Ras signaling pathway
          • neurofibromin deficiency leads to increased Ras activity
          • affects Ras-dependent MAPK activity which is essential for osteoclast function and survival
      • neurofibromatosis is the most common genetic disorder caused by a new mutation of a single gene
    • Associated conditions
      • scoliosis 
      • anterolateral bowing of tibia
      • bowing of forearm bones with obliteration of medullary cavity
        • ulnar pseudoarthrosis
        • radius pseudoarthrosis
      • neoplasias
  • Diagnosis
    • Diagnostic criteria
      • according to the NIH Consensus Development Conference Statement (1987) the diagnostic criteria for NF-1 are met in an individual if two or more of the following are found
        • six or more café-au-lait macules over 5 mm in greatest diameter in prepubertal individuals and over 15 mm in postpubertal individuals.
        • two or more neurofibromas of any type or one plexiform neurofibroma.
        • freckling in the axillary or inguinal region.
        • optic glioma.
        • two or more Lisch nodules (iris hamartomas).
        • a distinctive osseous lesion such as sphenoid dysplasia or thinning of long bone cortex with or without pseudarthrosis.
        • a first-degree relative (parent, sibling, or offspring) with NF-1 by the above criteria.is based on presence of both
  • Classification
    • NF1 (von Recklinghaussen disease)
      • most common
    • NF2
      • associated with bilateral vestibular schwannomas
    • Segmental NF
      • features of NF1 but involving a single body segment
  • Presentation General
    • Presentation
      • often presents with anterolateral bowing of tibia
      • often presents with radial bowing
    • Physical exam
      • verrucous hyperplasia
      • hemihypertrophy
      • cafe-au-lait spots
      • axillary freckling
      • scoliosis
      • anterolateral bowing or pseudoarthrosis of tibia
      • dermal Plexiform-type neurofibroma may be seen
      • Lisch nodules
        • are benign pigmented hamartomas of the iris
  • Neoplasias (Neurofibromatosis)
    • Neurofibromas (plexiform-type)
      • is pathognomonic for NF1
      • present in 4% of NF1
      • may be dermal or in deep tissues
      • often associated with limb overgrowth
      • can undergo malignant transformation to neurofibrosarcoma
    • Wilms Tumor
  • Scoliosis (Neurofibromatosis)
    • Introduction
      • spine is most common site of skeletal involvement in NF-1
        • scoliosis is NOT associated with NF-2
      • can take two forms
        • idiopathic-like form (nondystrophic)
          • longer curve and treatment resembles that for idiopathic scoliosis
        • dystrophic form
          • curve is typically thoracic kyphoscoliosis with a short segmented and sharp curve with distorted ribs and vertebrae
          • usually recognized earlier than nondystrophic form
          • generally characterized by a sharp angular curve involving 4 to 6 vertebrae
    • Imaging
      • radiographs show
        • vertebral scalloping
        • penciling of ribs (penciling of 3 or more ribs is a poor prognostic finding and associated with rapid curve progression)
        • enlarged foramina
      • MRI
        • always obtain preoperative MRI to identify dural ectasia and dumbbell lesion (neurofibroma on nerve root)
        • paraspinal masses are useful to distinguish from idiopathic scoliosis
    • Treatment
      • nonoperative
        • observation vs. bracing
          • bracing is not effective for dystrophic form
          • nondystrophic scoliosis in NF is treated like adolescent idiopathic scoliosis
      • operative
        • decompression, anterior spinal fusion (ASF) & posterior (PSF) with instrumentation
          • indications
            • dystrophic scoliosis
              • perform early in young children (< 7 yrs) with dystrophic curves
          • complications
            • high rate of pseudoarthrosis with PSF alone (40%)
              • pseudoarthrosis rate still high with ASF&PSF (10%)
              • some recommend augmenting the PSF with repeat iliac crest bone grafting 6 months after the primary surgery
  • Anterolateral Tibial Bowing (Neurofibromatosis)
    • Introduction
      • epidemiology
        • anterolateral bowing is often associated with neurofibromatosis (NF1)
        • 50% with anterolateral bowing have NF1
        • 10% of NF1 have anterolateral bowing
      • pathophysiology
        • may progress to pseudoarthrosis
      • differentials for tibia bowing
        • anteromedial
          • associated with fibular hemimelia and congenital loss of lateral rays of the foot
        • posteromedial
          • usually congenital due to
            • abnormal intrauterine positioning
            • dorsiflexed foot pressed against anterior tibia
            • will develop leg length discrepancy
            • associated with calcaneovalgus deformity
    • Imaging
      • radiographs
        • obtain AP and lateral of tib/fib
    • Treatment
      • nonoperative
        • bracing in total contact orthosis
          • indications
            • bowing without pseudoarthrosis or fracture (goal is to prevent further bowing and fractures)
            • spontaneous remodeling is not expected
            • osteotomy for bowing alone is contraindicated
      • operative
        • bone grafting with surgical fixation
          • indications
            • in bowing with pseudoarthrosis or fracture
        • amputation with prosthesis fitting
          • indications
            • three failed surgical attempts
            • Syme's often superior to BKA due to atrophic and scarred calf muscle in these patients
    • Techniques
      • intramedullary nailing with bone grafting
        • resect pseudoarthrosis
        • insert Charnley-Williams rod
        • antegrade through resection site, then retrograde through the heel
        • < 4 y.o., extend fixation to calcaneus
        • 5-10 y.o., extend fixation to talus
          • 2 yrs. postop, typically a 2nd surgery to push rod proximally to free the ankle joint
      • free fibular graft
        • often need to take fibula from contralateral side because ilpsilateral fibula is not normal
        • Illizarov's external fixation
  • Prognosis
    • Studies show between 8-10 years of decreased life expectancy compared to general population
    • High incidence of malignancy and hypertension
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