Variables affecting interpretation of skin prick test results.

BACKGROUND: Both performer- and device-dependent variabilities have been reported in sizes of wheal responses to skin prick tests. OBJECTIVE: We aimed to evaluate whether or not variabilities in sizes of wheal responses influence the final interpretation of skin prick tests; in other words, the decision on whether or not there is an allergy to a given antigen. METHODS: Skin prick tests with positive and negative controls and extracts of Dermatophagoides farinae and Dermatophagoides pteronyssinus were done for 69 patients by two different persons, using two different puncturing devices- disposable 22-gauge hypodermic needles and metal lancets. RESULTS: Among four different skin prick tests, the average coefficients of variation in sizes of wheal responses were near to or higher than 20% for all of them. On the other hand, in the final interpretation of results, kappa values indicated substantial or almost perfect agreements between these tests. However, the frequency of establishing allergy to the house dust mites widely ranged in these tests (20.8-35.8% for D. farinae and 20.8-28.3% for D. pteronyssinus). LIMITATIONS: The conduction of the study in a single center and the comparisons of results of only two performers. CONCLUSION: We feel that variabilities in sizes of wheal responses of skin prick test can influence its categorical results.

Histological changes in the nerve, skin and nasal mucosa of patients with primary neuritic leprosy.

Primary neuritic leprosy (PNL) presents as a peripheral neuropathy with no visible skin patches and skin smears negative for acid fast bacilli. The pathogenesis of PNL is poorly understood. The aim of the study was to document the histological changes in the nerve, apparently normal skin and nasal mucosa in PNL and to study its significance to the pathogenesis of leprosy lesions. The study is based on a cohort of 208 PNL patients registered at the Schieffelin Leprosy Research and Training Centre, Karigiri. All patients had a nerve biopsy, 196 had a skin biopsy and 39 had a nasal mucosal biopsy. The findings reveal that PNL patients exhibit a spectrum of disease histologically in the nerve ranging from lepromatous to tuberculoid leprosy with a significant proportion (46%) manifesting a multibacillary leprosy histology. Findings in the apparently normal skin and nasal mucosa reveal that there are widespread changes due to leprosy in tissues such as the skin and nasal mucosa even when the disease appears clinically confined to a few nerves. PNL may be an early stage in the pathogenesis of the disease before the appearance of skin lesions. The number of nerves enlarged and lepromin status did not give any clue to the nature of underlying disease.

[Detecting and monitoring leprosy neuropathy: which test to chose?]. / Dépister et surveiller une neuropathie hansénienne: quel test choisir?

The purpose of the study is to propose a simple and reproducible test for assessing nerve damage in leprosy. It is applied to the sensory branch of the radial nerve of leprosy patients, prior to any treatment. Skin sensitivity is measured by means of a needle, a drop of ether and some calibrated filaments. These three tests are collated and compared with the results of electromyographic examination of the nerve. The filament calibrated to 0.2 grams gives optimum sensitivity (0.79) and excellent specificity (0.95) in relation to the electromyographic test. Its routine use in the field is simple and reproducible and should result in a greater number of patients receiving the treatment they need.

Studies towards the standardization of lepromin. Progress and prospects.

Because of the wide range of concentrations of Mycobacterium leprae in existing lepromins the authors studied methods of producing a standardizable lepromin containing 160 million bacilli/ml. The effects of using different dilutions of lepromin on the incidence of false-positive reactions were also studied.Progress reported includes a convenient method for preparing large batches of non-sedimenting lepromin, which is directly suitable for microscopic counting of Myco. leprae cells; and a validation of current methods for microscopic enumeration of Myco. leprae. Skin tests with diluted lepromins have demonstrated that dilutions up to 1:16 increase progressively the ability to distinguish between lepromatous and tuberculoid leprosy. This work has provided further evidence that 20 million bacilli/ml (a 1:8 dilution of the initial lepromin) should produce adequate Mitsuda reactions in general populations, provided that 3-mm reactions are taken as the criterion for 1+ positivity. The net effect of these findings is equivalent to expanding the world supply of lepromin by 8 times.Recommendations for further research are proposed.