Pellagra is no longer the medico-social problem it was in the past. Nevertheless in countries with a low nutritional level it continues to a considerable degree in endemic form. However, in other countries with much sunlight the incidence of the disease is also high. The appearance of the syndrome is favoured by sunlight accentuating cases which under other conditions would remain subclinical. The mechanism for the biosynthesis of nicotinic acid in man as well as the histochemical and photobiological processes which take place at a cellular level in the skin are not fully understood. Pellagra is a clinical syndrome characterized by: (i) Symmetrical skin lesions located primarily on light-exposed areas. (2) Gastrointestinal anomalies. (3) Nervous and psychic disturbances. Not all of these need be present simultaneously, especially at the onset. Pellagra has occurred in many geographical areas as one of the commonest world-wide afflictions. It has now virtually been eradicated in the western world. This great advance in public health has been achieved by the improvement of nutrition and particularly by the enrichment of wheat flour with nicotinic acid. Although to-day the condition is rather uncommon, occasional cases are found. It is still endemic in remote areas of the world where green vegetables, fruit and animal proteins are unobtainable. In areas of the so-called 'civilized world' where nutritional problems do not really exist, pellagra is occasionally found in individuals with psychiatric disorders, alcoholics, recluses or elderly widowers who have an improper food intake. The well known group of symptoms traditionally remembered as Pellagra's four D's—dermatitis-diarrhoea-dementia and when untreated, death—is very seldom seen. Most cases are less typical and are borderline in nature. According to Barret-Connor (1967) pellagra appears in an endemic form in Egypt, mainly in the area of the Nile-delta, but information from Egypt is rather controversial. According to Abdou (1965) it appears in a mild form despite the fact that it is still endemic in Egypt, and does not constitute the severe problem of the past. This improvement is due, he believed, to the gradual replacement of maize by wheat. Thus, during the years 1947-48, the wheat-maize ratio was o 75 whereas in 1965 it had increased to i-2 and more wheat was being consumed by the rural population. Khattab et al. (1967) and Hanafy et al. (1968) supported the concept that the disease is rather common in Egypt, mainly among the poor rural population and with a higher incidence in the prepubertal and pubertal age groups. In a statistical study carried out in 1952 in Kalyuba (an area of Egypt) 9-12% of the children aged 5-9 years and 12-21% of the children aged 10-19 years had the disease (Darby, 1952). More recent reports by El Zawahry & El Zawahry (1972) stated that the disease is now rare in Egypt. In areas of Africa south of the Sahara, namely in Nyasaland (Malawi), Basutoland (Lesotho), as well as areas of South Africa where maize is still a basic food, pellagra continues to an exceedingly high degree. In 1956 a WHO review stated that pellagra was the most common deficiency disease and that, during the worst season (from October till February), 15% of the population was suffering from it (Aykroyd, 1971).

Pellagra: a still existing disease

The true incidence of drug-induced photosensitivity is unknown. It seems likely that variations in reported incidence may be explained by local variations in skin type, sunlight factors, and drug dosage regimens. Unfortunately, only a small number of drugs have been studied in detail, so firm data are often unavailable to satisfy a number of points essential for patient management. Such information includes which drugs are responsible for abnormal skin reactions to sunlight, the morphology of the reaction produced, the mechanisms involved in the reactions, the wavelength dependency of the reaction produced, and long term effects if observed.' Photosensitivity reactions to exogenous chemicals occur after exposure to both the specific compound and either UVR or visible radiation. The chemical exposure may be topical or systemic, but the presence of the chemical within the skin during exposure to the radiation is required. A particular drug will absorb radiation within a certain spectral range. UVA is most frequently implicated, perhaps due to its greater penetration into the dermis. Classically, photoinduced drug eruptions have been divided into two types based on the proposed mechanism of the reaction: phototoxicity and photoallergy.^

Photodermatoses. part ii: chemical photodermatoses and dermatoses that can be exacerbated, precipitated, or provoked by light

La quantite de porphyrins faecaux et sanguins trouvee dans 21 cas de pellagrins normale comparee a celle des cas normaux observes en Egypte. Cependant, dans 5 cas les porphyrins sanguins et faecaux furent plus nombreux et les porphyrins urinaires resterent en quantite normale.

Porphyrin metabolism in pellagra.

Pellagra and its treatment with nicotinic acid and nicotinamide with a review of the literature.

SIR,—^We were puzzled that the natural keratotic pellagrous lesion showed coarse cracking and the experimentally induced lesion did not (Findlay et al., 1969). Two possible reasons were—(a) the experimental lesions were shielded from the dry outdoor climate, (b) the cracking was due to a solid pile-up of hastily keratinized and adherent cells whieh dissected off with difficulty and cracked into large plates before being shed. A third possibility, not at the time considered by us, was an alteration in the nonkeratinovis hygroscopic substances in the keratinizing epithelium. Sims and Hall (1968) suggested that the polypeptides (keratins predominantly) were less well cross-linked in malnutrition, leading to a readier uptake and presumably a readier loss of water. This would support the first contention given above. Middleton (1968) shifted the emphasis on the hygroscopic properties of the stratum corneum away from the structural proteins to the water soluble substances trapped in the cornified cell residua. Such a proposal means that the hygroscopic properties of hair may no longer be comparable. This author limited his special observations to relative humidities of 80% and more, whieh takes them out of our cHmate range for the cracking of pellagrous skin. The curves he gives of water uptake at lower humidities are not very different from those of hair. The non-polypeptide fraction of the stratum corneum has therefore little proven significance in water-binding at lower humidities. Sorption isotherms of sealp hair (each in duplicate) from 14 Bantu children were compared with 14 Bantu cases of kwashiorkor with manifest thinning, straightening and lightening of the hair. Zero humidity weights were determined over phosphorus pentoxide and hydrated weights at relative humidities of 10, 25, 50, 75 and 90% over sulphuric acid solutions of the appropriate vapour pressure at 25° C. (SpencerGregory and Rourke, 1957), and 100% over water. Up to 5 days was allowed for slow equilibration. There was no difference in the weight increases of the normal and abnormaJ groups over a physiological range. From 10-75% RH the weight gain from water binding was identical and virtually linear, between a 3% increase over the dry weight at 10% RH to a 15% increase on the dry weight at 75% RH. From 75-100% there was a sharp rise with a broad scatter of 20-70% above dry weight regardless of the source of the specimen, and regardless of prehminary ether-washing of a few of the specimens. The findings differ very little from those of sheep wool (Alexander and Hudson, 1954). Abnormal corneum scales from 1 pellagra and 2 kwashiorkor eases similarly examined showed no great differences (weight gain 2-4% at 10% RH and 11-14% at 75% RH). A further experiment was perii'ormed on the horny layer prepared by Middleton's procedure from the skin of 7 normal human subjects (5 Bantu, 2 white) and 3 samples of normal stratum corneum from pellagra subjects along with the scraped-off scales from the same patients. Duplicate samples were respectively (i) dried, washed in water for 6 hr., dried and then tested for water uptake, and (ii) dried, washed in chloroformmethanol (2 : 1) for 20 hr., washed in water for 6hr., dried and then tested for water uptake. RH of 75 and 90% only were studied and compared. The results were unexpected: at both RH values the specimens had roughly 25% more water uptake in them after defatting and washing than those which had been washed alone. A loss of hygroscopic power through defatting and washing was not found in any specimen. We therefore have no evidence for disturbed water binding of the horny skin structures in human malnutrition.

Is the cracking in pellagrous hyperkeratoses due to disturbed water binding.

SUMMARY. In dark skinned subjects, delayed or “secondary” pigmentation from ultra-violet light may be the only clinical sign of sunburn. It results from necrobiosis limited to the outer Malpighian layer and hardly extends deeper than this even when the dose exceeds the maximum possible from a day's natural sunshine. Preceding erythema is not merely masked by the pigment, but is often virtually absent. On the background of this natural skin resistance, the hyperkeratotic pellagrous lesion is interpreted as a marked reaction to mild or repeated ultraviolet injury followed by retention and ultimate cracking of the abnormal layers so produced. These layers are formed below the normal stratum granulosum when the initial damage is severe, but lie above the new stratum granulosum which forms underneath as the cells keratinize.

Reactions to light on the normal and pellagrous Bantu skin.

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Reactions to light on the normal and pellagrous Bantu skin.