Bilateral simultaneous disc edema and cataract associated with albright hereditary osteodystrophy.

A 16-year-old female presented with poor vision in both eyes. On clinical examination, she had bilateral cataracts and optic disc edema bilaterally on ultrasound examination. Extensive intracranial calcification was evident on computerized tomography. Physical examination revealed short stature, rounded chubby face, dental abnormalities, brachydactyly, and obesity. Laboratory evidence of hypocalcemia, hyperphosphatemia, elevated parathyroid hormone level (indicative of pseudohypoparathyroidism) along with the constellation of phenotypical characteristics lead to a diagnosis of Albright's hereditary osteodystrophy. This case is being presented to increase awareness regarding presence of coexisting and previously undiagnosed hypocalcemic syndromes in pediatric cataracts. The role of an ophthalmologist may be pivotal in diagnosing such an entity as documented in the present case.

INTRODUCTION

Albright's hereditary osteodystrophy (AHO) is a rare inherited metabolic disorder characterized by a typical phenotype. It is associated with hypocalcemia with or without resistance to parathyroid hormone (PTH, pseudohypoparathyroidism [PHP]). We report a rare case of simultaneous bilateral optic disc edema with cataracts associated with AHO.

CASE REPORT

A 16-year-old female presented with painless progressive diminution of vision in both eyes for a period of six months. A history of poor growth velocity, tooth decay, tooth loss and misalignment, defective hearing, global developmental delay during childhood, and poor scholastic performance was elicited. Medical history was significant for seizures over the past four years. The menstrual history was normal with menarche at 14 years. She was the product of a nonconsanguineous union and was delivered at home with no significant complaints in the neonatal period.

On ocular examination, visual acuity was 1/60 OU. Anterior segment was remarkable for presence of bilateral total white cataracts [Figure 1a] with normal pupillary reactions. Posterior segment evaluation by B-scan ultrasound revealed bilateral optic disc edema without optic disc drusen.

Figure 1

(a) Diffuse slit lamp photograph of right eye with total white cataract. (b) Postoperative fundus photograph of the right eye showing disc edema

On general physical examination, she had short stature (138 cm, 80% of expected), rounded chubby face [Figure 2a], short stubby hands and feet (brachydactyly), especially the fourth and fifth metacarpals, and obesity (body mass index of 25.26). Chvostek's sign (twitching of facial muscles after tapping the facial nerve just in front of the ear) and Trousseau sign (carpal spasm after maintaining an arm blood pressure cuff at 20 mm Hg above the patient's systolic blood pressure for 3 minutes) were demonstrable. Examination of the oral cavity showed hypodontia and misaligned teeth [Figure 2b]. Her sexual maturity rating was Tanner's stage III.

Figure 2

(a) Rounded chubby face. (b) Oral cavity examination showing hypodontia and misaligned teeth

A computerized tomographic scan of the brain showed extensive intracranial calcifications bilaterally [Figure 3]. An electrocardiogram showed prolongation of QT interval. The biochemical profile revealed hypocalcemia (Ca2+ 7.3 mg/dl; normal range, 8.5-10.2 mg/dl), hyperphosphatemia (S. PO43- 6.7 mg/dl; normal range, 2.5-4.1 mg/dl), normal alkaline phosphatase (15 KAU; normal range, 2-17 KAU), normal serum creatinine (0.8 mg/dl), and markedly elevated serum PTH level (526 pg/ml; normal range, 10-60 pg/ml) indicative of resistance to PTH (PHP). Further subtyping was deferred due to nonavailability of tests for urinary cyclic AMP excretion and Gs alpha activity in the erythrocyte membranes. Serum thyroid-stimulating hormone, adrenocorticotropic hormone, growth hormone, and gonadotropin levels were within the normal range for the testing laboratory.

Figure 3

Plain computerized tomographic scan of the brain showing intracranial calcification in bilateral basal ganglia (thick arrow), thalamus and subthalamic nuclei (thin arrow), and cerebral white matter (arrow heads)

The constellation of characteristic phenotypic, imaging, and biochemical profile was typical of AHO. The patient was started on combination therapy of oral calcium and vitamin D3 (calcitriol) along with an antiseizure medication in consultation with an endocrinologist. She underwent uneventful lens aspiration with intraocular lens implantation in the right eye under local anesthesia. The postoperative visual acuity improved to 6/9 and fundus evaluation confirmed the optic disc edema [Figure 1b]. At 3 months postoperatively, she underwent cataract surgery for the left eye. Fundus examination at this time revealed complete resolution of disc edema bilaterally. In addition, the child's general well being had improved.

DISCUSSION

Important causes of hypocalcemia in childhood include hypoparathyroidism, PHP, chronic renal failure, and vitamin D-dependant rickets. PHP (OMIM #103580 and #103580) refers to a heterogeneous group of disorders characterized by hypocalcemia, hyperphosphatemia, increased serum concentration of PTH, and insensitivity to the biological activity of PTH.1

AHO is a form of PHP that is often associated with a characteristic phenotype of rounded face with a short, stocky stature. Brachydactyly is the most reliable physical sign of AHO and was seen in our patient .2 Several other skeletal deformities have been described in AHO, including short ulna, bowed radius, deformed elbow, or cubitus valgus and coxa vara, coxa valga, genu varum, and genu valgum deformities.3 Dental anomalies are present in the form of enamel defects, hypodontia, and caries as demonstrated in our patient.4 Mild mental retardation and basal ganglia calcification are found later in life.5

The development of cataract in AHO occurs in the second decade and is thought to be due to disturbance in the calcium metabolism causing lenticular opacification. There is evidence that the cataract is related to the level of hypocalcemia and does not depend on the duration of the disease.6 A multifactorial etiology for bilateral disc edema can be postulated, such as impaired axoplasmic conduction due to reduced calcium and stasis, impaired CNS vascular autoregulation causing venous stasis, and raised intracranial pressure due to pseudotumor cerebri.7 The papilledema in hypocalcemia does not behave like that due to intracranial space occupying lesion or cerebral venous thrombosis. The disc edema readily responds to calcium therapy and disappears with calcium levels higher than 8 mg/dl, as seen in our patient.8

Molecular defects in the GNAS1 gene on chromosome 20, which encodes Gs-alpha (OMIM number #139320), contribute to at least four different forms of the disease, which are as follows: PHP type 1a, PHP type 1b, PHP type 2, and pseudo-PHP.9 Patients with PHP 1a are labeled AHO and have characteristic phenotype described above, resistance to G-protein-coupled hormones, attenuated response in urinary phosphate and cAMP excretion after intravenous infusion of synthetic PTH, and a decreased Gs-alpha activity in erythrocytes.

Full expression in AHO is associated with inheritance of the maternally transmitted allele, although inheritance of the paternally transmitted allele results in partial expression irrespective of the expression in the parent. The differential effect of the gene depending on whether it is maternally or paternally transmitted suggests a role for genetic imprinting in AHO, as has been suggested in certain other conditions with dominant inheritance.1011

In conclusion, a high level of suspicion for metabolic disturbances is needed by an ophthalmologist while evaluating a case of bilateral cataract and disc edema in adolescents. Hypocalcemia may present with cataract as the initial manifestation. Simultaneous bilateral optic disc edema and cataract is an exceedingly rare manifestation of hypocalcemia, and to our knowledge, have never been reported together.