A practical approach to interpretation of corneal specimens.

Corneal specimens form only a small part of the routine practice for most histopathologists but their assessment often requires considerable effort and specialized knowledge. The most common corneal specimens, full-thickness corneal discs and corneal biopsies, are discussed in this review. Corneal discs removed at keratoplasty are non-urgent specimens, as definitive treatment has already been undertaken, and while the pathologic diagnosis may change the prognosis for the graft, it rarely affects immediate treatment. Accurate diagnosis is still important, and will affect counseling of the patient, but referral to a colleague with a special interest is possible if necessary. Conversely, small partial-thickness corneal biopsies, which are mostly undertaken for culture negative keratitis with underlying suspected infection, are very urgent. Infectious keratitis can follow an extremely aggressive course, resulting in destruction of the cornea within hours. Accurate diagnosis is imperative. Due to the urgency of such specimens and the importance of diagnosis for immediate treatment, referral is not usually possible. It is the role of the pathologist to make optimal use of a small specimen to reach the relevant diagnosis in the minimum space of time.

Crystalloidal paraprotein deposits in the cornea: an ultrastructural study of two new cases with tubular crystalloids that contain IgG kappa light chains and IgG gamma heavy chains.

The fine structure and immunoprotein content of the crystalloids are described in two cases of paraproteinemic crystalloidal keretopathy, both of which had clinical features thought by the referring ophthalmologists to be those of atypical lattice-type corneal dystrophy (presumably because of lattice-like lines). Most keratocytes in one case were surrounded by a mantle of densely packed tubular crystalloids. Individual tubules were annular in cross section with mean dimensions as follows: overall diameter, 29.32 nm (SD 1.26); internal diameter (core), 8.53 nm (SD 1.12); wall thickness, 10.39 nm (SD 0.85) (n = 10). Crystalloids were extracellular and found only in the corneal stroma, with none in Bowman's layer or Descemet's membrane. In the second case, the tubules had a similar distribution but formed geometric arrays with no clear relationship to, or envelopment of the keratocytes. The tubules were thin-walled, with mean dimensions as follows: overall diameter, 26.12 nm (SD 1.12); internal diameter (core), 15.46 nm (SD 1.12); wall thickness, 5.33 nm (SD 0) (n = 10). In both cases the tubules were kappa-light chain- and gamma-chain-positive. Laboratory investigations revealed the presence of two IgM-kappa paraproteins and an IgG-kappa paraprotein in the serum of the first patient. The second patient had an IgG-kappa paraproteinemia and bone marrow changes consistent with low-grade non-Hodgkin's lymphoma. These cases emphasize and extend the morphological range of corneal IgG crystalloids; the second case also demonstrates that corneal IgG crystalloids may be an early indicator of un underlying immunoproliferative disease.

Paraproteinemic crystalloidal keratopathy: an ultrastructural study of two cases, including immunoelectron microscopy.

The ultrastructural appearances of corneal crystalloidal deposits are described in two patients with an IgG-kappa paraproteinemia of uncertain pathogenesis. The crystalloids in one patient were overwhelmingly intracellular and were found mainly in stromal keratocytes, but also in basal corneal epithelial cells and the limbal vascular endothelium. Four types of crystalloid or immunoprotein-containing granules were recognizable in this case: 1) fibrillary crystalloids with a curvilinear filamentous substructure; 2) angulated geometric crystalloids that often had a linear filamentous substructure and transverse or oblique periodicity; 3) cordlike crystalloids; and 4) lysosomelike granules with amorphous contents. Immunoelectron microscopy demonstrated that all of these structures labeled for kappa-light chains, and rectangular type 2 crystalloids showed approximately a twofold greater concentration of the colloidal gold probe than the type 1 fibrillary crystalloids. The evidence suggested development of the crystalloids within lysosomes, with a progression from the granules containing amorphous material, through fibrillary crystalloids, to the geometric structures. The circumferential distribution of the corneal deposits, as well as the presence of vascular endothelial crystalloids and reduplication of external laminae around limbal blood vessels, suggests that the crystalloids originated predominantly or entirely from the blood, with transport of immunoprotein across damaged limbal microvasculature. The abnormal vasculature may also have contributed to corneal edema, which in turn may have exacerbated corneal opacification. The crystalloidal deposits in the other case were exclusively extracellular; they were located beneath and between corneal basal epithelial cells, and predominantly as a mantle around individual keratocytes. The crystalloids in this case consisted overwhelmingly of thick-walled tubules about 40 nm in diameter that labeled for both kappa-light chains and gamma chains with the colloidal gold immunoprobe. In addition, lucent vesicles within keratocytes were found only in sections labeled for kappa-light chains and were positive. The factors that might contribute to the formation of corneal crystalloidal deposits in immunoproliferative disorders are discussed, and include: 1) an inherent propensity for crystallization of some immunoglobulins or kappa-light chains, perhaps because of abnormal molecular structure; and 2) local factors in the cornea that might promote deposition and crystallization of immunoprotein, such as temperature, pH, the water content, and extracellular matrix components.

Infection in experimental arthroplasties.

Experimental bacterial infection following implant arthroplasties was investigated in rabbits. Bone cement and a stainless steel head and stem prosthesis were inserted after reaming of the femoral neck and shaft. Measured doses of Staphylococcus aureus were injected either into the femoral medullary cavity or intravenously. Intravenous challenge required high inocula to establish arthroplasty infection, whereas infection around the prosthesis was consistently established after inoculation of 10(3) bacteria into the femoral medulla. The erythrocyte sedimentation rate (ESR) proved the most reliable clinical test of infection. Hematogenous infection was difficult to reproduce. Three weeks after operation, the arthroplasty was as resistant as the normal hip. Antibiotics were administered in doses equivalent to doses used in the treatment of infections in humans. When gentamicin-impregnated cement was used, 60 times the number of organisms were required to establish infection. Flucloxacillin and Imipenem gave similar protection. Rifampicin gave protection to a level exceeding the lethal dose of organisms for the model.

The subcutaneous air pouch model of synovium and the inflammatory response to heat aggregated gammaglobulin.

Subcutaneous injection of sterile air in rodents results in the formation of an air pouch with a lining morphologically similar to synovium (Edwards et al., 1981). We extended the comparison between pouch and synovial tissue and confirmed broad similarities in structure and function but also noted important differences. The air pouch was used to study the time course of the acute inflammatory response to heat aggregated human IgG. Saline washout of the pouch allowed simultaneous measurement of cellular and mediator components of the inflammatory exudate. The aggregates were rapidly phagocytosed by the pouch lining cells, resulting in acute inflammation characterised by polymorphonuclear leucocyte infiltration with peak numbers in the exudate at 12 hours, temporally dissociated from the earlier peak of PGE2 at 3 hours.

Crystal shedding in septic arthritis: case reports and in vivo evidence in an animal model.

Two cases of coexisting septic and crystalline joint disease are reported. In one patient polyarticular septic arthritis occurred simultaneously with gout and pseudogout. In a second patient septic arthritis preceded the appearance of calcium pyrophosphate dihydrate (CPPD) crystals in the joint fluid, supporting an earlier postulate that lysosomal enzymes released during sepsis lead to shedding of crystals from cartilage and synovium into the joint space. This sequence was demonstrated in a rat air pouch model of synovium, in which CPPD crystals embedded in facsimile synovial tissue were released after injection of pyogenic bacteria. Coexisting septic arthritis should always be considered when crystals are identified in inflamed joints, particularly in elderly patients with concurrent infections.

Infection in experimental hip arthroplasties.

The relationship between the route of inoculation, the dose of inoculum and the development of infection after prosthetic replacement has been determined in an animal model. The rabbit hip served as the model and a Staphylococcus aureus isolated from an infected human hip arthroplasty was introduced using different protocols. The 50% infective dose (ID50) was determined for comparative purposes. Contamination of the wound site with only a few bacteria was likely to result in infection. It was considerably more difficult to induce infection when the operation was performed without inserting the prosthesis, which suggests that the implant inhibits the body's mechanism for dealing with the insult. It was difficult to produce infection by inoculating the organisms into the bloodstream: if this inoculation was delayed till three weeks after operation the animals were often grossly septicaemic by the time the arthroplasty was infected. The results emphasise the importance of minimising intra-operative contamination and the efficacy of antibiotic cover.

Pigmented villonodular synovitis associated with psoriatic polyarthropathy: and electron microscopic and immunocytochemical study.

A case of pigmented villonodular synovitis in a patient with psoriatic polyarthropathy was studied by means of light microscopy, electron microscopy and immunocytochemical techniques. The lesion consisted of mononuclear phagocytes with features intermediate between type A and type B cells, two types of multinucleate giant cells, an abnormal vasculature, extravasated fibrin and erythrocytes. An unexpected feature was the presence of a mononuclear cell whose cytoplasm contained intermediate filaments and reacted strongly to antisera to cytokeratins. Such a cell type has not previously been described in this condition and its significance is unclear. The findings support the theory that the pathogenesis of PVNS involves leakage of blood through abnormal vessels resulting in the local accumulation and proliferation of mononuclear phagocytes, connective tissue cells and unidentified cytokeratin positive mononuclear cells. The aetiology of the vascular damage, however, remains unknown.