Delayed type IV hypersensitivity reaction to porcine acellular dermal matrix masquerading as infection resulting in multiple debridements.

INTRODUCTION: Delayed type IV hypersensitivity reactions are well established in the surgical setting with respect to external exposure via topical antibiotics and internal exposure via synthetic materials. In contrast, biologic matrix is derived from decellularized human or animal tissues and is consequently believed to elicit a minimal host inflammatory response. OBJECTIVE: We report a case of delayed type IV hypersensitivity reaction secondary to a biologic comprised of porcine-derived acellular dermal matrix, [Strattice™]. CONCLUSIONS: While biologic matrix is often preferred over synthetic mesh due to its decreased risk for infection, this case emphasizes that potential for hypersensitivity to the material persists. Type IV hypersensitivity reactions should be included in the differential diagnosis for suspected post-operative infections.

A new liquid formulation of 8-methoxypsoralen: bioactivity and effect of diet.

A new encapsulated liquid preparation of methoxsalen (8-MOP) and a commonly used crystalline preparation (Oxsoralen) were compared in 12 subjects. Each subject ingested 0.6 mg/kg body weight of each formulation on different days. Six subjects ingested a low-fat meal before ingestion of drug, and 6 subjects ingested a high-fat meal. Photosensitivity was tested from 1/2 to 6 h after ingestion of 8-MOP by exposure to 320-400 nm radiation (UVA) from a filtered xenon are lamp. A series of graduated doses of UVA were administered at each time point to determine the minimum phototoxic dose (MPD). Ingestion of 8-MOP and grading of erythema were conducted in a double-blind manner, and bilaterally symmetrical exposure sites were used to test each preparation. The phototoxic reaction was observed at 24, 48, and 72 h by two experienced observers who were unaware which formulation had been ingested. The two test days were separated by 48 h. The encapsulated liquid preparation induced greater photosensitivity than Oxsoralen (mean MPDs +/- SD: 7.1 +/- 4.7 vs 12.9 +/- 6.7 J/cm2, respectively; n = 12; p less than 0.05). The encapsulated liquid preparation also induced photosensitivity earlier than Oxsoralen (mean hours after ingestion to achieve peak photosensitivity +/- SD: 2.1 +/- 1.2 vs 3.9 +/- 1.6, respectively; n = 9; borderline significance). On a low-fat diet the encapsulated liquid peaked 2.5 h earlier than Oxsoralen, as well as showing the shortest and the most predictable period of photosensitivity. However, overall, the degree and time of peak photosensitivity induced by either preparation were unaffected by diet. Ingestion of the encapsulated liquid induced photosensitivity in all 12 subjects; Oxsoralen failed to sensitize 3 subjects. Side effects were similar after both preparations. A new encapsulated liquid preparation of 8-MOP may thus allow lower doses of UVA to achieve therapeutic results in photochemotherapy, and a shortened waiting period following ingestion of drug.

Cutaneous photosensitization by 8-methoxypsoralen: order-dependent synergism between radiation less than 380 nm and broadband UVA.

Human skin treated with topical 8-methoxypsoralen (8-MOP) was exposed sequentially to radiation at wave-lengths longer than 380 nm and to broadband UVA (320-400 nm). A striking, order-dependent synergism with respect to the induction of cutaneous phototoxicity as measured by delayed erythema was present. When exposure to greater than 380 nm radiation preceded exposure to broadband UVA, the effect was synergistic. When the order was reversed, the effect was approximately additive. This synergism is best explained by UVA-induced conversion to DNA cross-links of the monoadducts formed by prior exposure at greater than 380 nm. The direct implication is that cross-linking of DNA by psoralen is the major important event in cutaneous phototoxicity due to psoralens. Skin treated with 8-MOP and markedly suberythemogenic doses of radiation greater than 380 nm remained synergistically sensitized to small doses of UVA for at least 72 h, long after photosensitization by 8-MOP alone had disappeared in control sites. This suggests slow in vivo repair of those psoralen-DNA monoadducts capable of being subsequently converted to DNA cross-links.

Fragmentation of biliary calculi with tunable dye lasers.

The feasibility of using lasers to fragment biliary calculi was examined in vitro. Flashlamp-pumped tunable dye lasers were coupled to small-diameter flexible quartz fibers that were placed in direct contact with biliary calculi. The minimum laser energy necessary to damage a calculus was measured for wavelengths between 450 and 700 nm and for pulse durations between 0.8 and 360 microseconds. This threshold energy increased with increasing wavelength but was not significantly affected by pulse duration. Cholesterol stones had uniformly higher thresholds than pigmented ones. When a repetitively pulsed laser was used, complete fragmentation required fewer than 500 pulses and fragments were predominantly less than 2 mm. The pulsed dye laser can effectively fragment biliary calculi when transmitted through a small-diameter quartz fiber and may be useful as a tool for fragmenting retained common duct stones.