Recurrence of Thiel-Behnke corneal dystrophy: an electron microscopic study

The hereditary Thiel-Behnke corneal dystrophy, first described in 1967,¹ is frequently confused with Reis-Bucklers dystrophy. Both conditions affect Bowman’s layer and can be difficult to differentiate both clinically and histopathologically. Previously, electron microscopic studies of corneal dystrophies affecting Bowman’s layer identified characteristic “curly fibres,” but it was unclear whether these were diagnostic of Thiel-Behnke or Reis-Bucklers.² More recently, Kuchle et al have attempted to clarify the situation, identifying these corneal dystrophies as two separate disease entities, and proposing the less confusing nomenclature of corneal dystrophy of Bowman’s layer (CDB) type 1 (geographic or “true” Reis-Bucklers dystrophy) and CDB type II (honeycomb or Thiel-Behnke dystrophy).³ In this report we present a case of Thiel-Behnke dystrophy diagnosed by electron microscopy after recurrence in the corneal graft. This case illustrates the diagnostic difficulties surrounding corneal dystrophies of Bowman’s layer, and highlights the continuing importance of electron microscopy as a diagnostic tool.

CASE REPORT

Following diagnosis of a familial corneal dystrophy, our patient underwent a left penetrating keratoplasty in 1967 at another hospital, at the age of 34 years. Although the pathological report of this was not available to us, the dystrophy was labelled “lattice type.” The following year her care was transferred to our hospital. At this time she was found to have a clear graft in the left eye with a visual acuity of 6/9, and multiple granular honeycomb-shaped corneal opacities at the level of Bowman’s layer in the right eye with a visual acuity of 6/12. By 1981 her right visual acuity had deteriorated to 6/18 so she underwent right penetrating keratoplasty. The pathology report commented on subepithelial fibrosis and patchy destruction of Bowman’s membrane, in keeping with Reis-Bucklers corneal dystrophy or possibly Salzmann’s dystrophy (fig 1). Lattice, macular and granular dystrophies were excluded with appropriate stains.

Figure 1.

 Corneal graft showing apparent subepithelial fibrosis (arrow). Masson’s Trichrome, magnification ×400.

Following a period of care at another hospital, she was re-referred to our hospital in 1999 with deteriorating visual acuity secondary to possible recurrence of the corneal dystrophy in both grafts. Best corrected visual acuities were 6/24 and 6/36 in the right and left eyes, respectively. Subepithelial corneal opacities were noted in the peripheral portions of both grafts (fig 2). She was also noted to have bilateral cataracts, so underwent right phacoemulsification in 2000. Postoperative recovery was uneventful, with visual acuity improving to 6/12. In 2002 complicated left cataract surgery led to graft decompensation requiring repeat grafting in 2003. Histopathology revealed apparent subepithelial fibrosis associated with patchy loss of Bowman’s layer. The endothelium was found to be markedly attenuated. Review of the previous pathology section from 1981 showed the apparent subepithelial fibrosis to be similar in both samples. Electron microscopy of both samples revealed the presence of “curly fibres” beneath the basal epithelium (fig 3), leading to the diagnosis of Thiel-Behnke corneal dystrophy with recurrence in the graft.

Figure 2.

 Slit lamp biomicroscopy showing recurrence of the “honeycomb” deposits in the corneal graft.

Figure 3.

 (A) Transmission electron microscopy showing the location of the “curly fibres” beneath the epithelium (arrow). Magnification ×4000 (B) “Curly fibres” seen at higher magnification (×12 000).

COMMENT

Owing to confusion surrounding the nomenclature of corneal dystrophies of Bowman’s layer, this patient was diagnosed as having Reis-Bucklers corneal dystrophy in 1981 following histological analysis of her right corneal button. However, the clinical picture is more in keeping with that described for Thiel-Behnke dystrophy with later, moderate visual loss and honeycomb-shaped opacities at the level of Bowman’s layer. The geographical opacities seen in Reis-Bucklers dystrophy are associated with early, marked visual loss, therefore differentiation between these dystrophies is important for the patient’s visual prognosis.³ The discovery of the characteristic curly fibres of Thiel-Behnke dystrophy on electron microscopy of both corneal buttons illustrates the importance of electron microscopy in the diagnosis of corneal dystrophies.