Phakomatoses

Chapter 65 Phakomatoses






Neurofibromatoses


The neurofibromatoses (NF) are diverse genetic conditions with a predisposition for tumor development. The two main types are neurofibromatosis type 1 (NF1) and type 2 (NF2).



Neurofibromatosis type 1


NF1 is a progressive disease and the final manifestations are extremely variable. Existing lesions tend to enlarge gradually and new lesions develop. The National Institutes of Health (NIH) diagnostic criteria are listed in Box 65.1.






Lisch nodules


Lisch nodules (melanocytic hamartomas) are dome-shaped, discrete lesions on the anterior surface of the iris or in the angle, usually bilateral. They are usually orange-brown (Fig. 65.1), appearing darker than blue irides but paler than brown irides (Fig. 65.2). Most are round and evenly distributed on the iris. Their size varies from a pinpoint to involvement of a segment of iris, sometimes confluent. In NF1, they are present in one-third of 2.5-year-olds, half of 5-year-olds, three-quarters of 15-year-olds, and almost all adults over 30.3 They occur earlier than neurofibromas and are, therefore, a useful marker for NF1. They need to be distinguished from iris nevi.






Skin, lids and orbits


Café-au-lait spots are hyperpigmented macular skin lesions, mostly present at birth and all appear by 1 year, enlarging at puberty. Common on the trunk, they are absent from the scalp, eyebrows, palms, and soles (Fig. 65.4). Histologically, there is melanocytic hyperplasia with increased pigmentation in the basal layer of the epidermis.



Neurofibromas are present in 30–50% of NF1 patients.4 They are network-like tumor growths involving multiple fascicles of nerve(s); four types are recognized (Table 65.1). The presence and growth pattern of neurofibromas is age related; in infancy and early childhood, diffuse plexiform neurofibromas are most active giving rise to cosmetic and visual problems within the orbit. Cutaneous or subcutaneous neurofibromas develop and grow fastest at puberty, the late teens, and during pregnancy. There is a lifelong risk of malignant transformation with poor prognosis for 5-year survival.5


Table 65.1 – Neurofibroma clinical features4























Neurofibroma types Location Clinical signs
Discrete cutaneous Epidermis and dermis Moves with skin, blueish tinge
Subcutaneous Deep to dermis Skin moves over, firm and rounded feel, located along peripheral nerves
Nodular plexiform Localized interdigitation with normal tissues “Bag of worms” feel (Figs 65.5, 65.6)
Diffuse plexiform Infiltrate widely and deeply Smooth, slightly irregular skin thickening



Complete surgical resection of plexiform neurofibromas is difficult due to their large size, location, local invasiveness, or involvement of critical peripheral nerves. Regrowth following subtotal resection is common. Chemotherapy is not effective. Promising clinical trials with biologic agents are underway.6






Neurofibromatosis type 2


Neurofibromatosis type 2 (NF2) affects 1 in 35 000 live births and is characterized by bilateral vestibular schwannomas, multiple central nervous system (CNS) tumors, cataracts, and retinal abnormalities. The diagnostic criteria for NF2 are shown in Box 65.2. Two patterns of presentation exist. Mild disease presents late (> 25 years), with few tumors other than bilateral vestibular schwannoma, and slow progression. Those with severe disease have onset before age 25, multiple CNS tumors (at least two of one type), and rapid progression, severe handicap or death before reproductive age. Treatment is multidisciplinary because of the complexities of the multiple and progressive lesions.7






Ocular findings


Most of the ophthalmic findings in NF2 (see Box 65.2) are congenital but may become more symptomatic over time.9 Visual loss increases morbidity since progressive bilateral hearing loss is so common in this condition.




Jun 4, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on Phakomatoses
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