Histopathology of Post Kala-azar Dermal Leishmaniasis

Abstract

The various lesions seen in the clinical presentation of post kala-azar dermal leishmaniasis (PKDL) are reflected in the histopathology of the type of lesion biopsied. The cells that form the dermal infiltrate include lymphocytes, histiocytes, and plasma cells in varying proportions. The infiltrate, which is mild and confined to the superficial dermis in macular lesion becomes denser with the increasing severity of the lesion. Leishman–Donovan bodies (LDB) in general are rarely demonstrable in macules and somewhat infrequently in the rest, though at times they may be numerous; mucosal lesions offer a greater chance of visualizing LDB than biopsies from the skin. A characteristic histomorphology in nodules is prominent follicular plugging with a dense plasma cell-rich lymphohistiocytic dermal infiltrate that shows an abrupt cut-off in the lower dermis, an appearance highly suggestive of PKDL even in the absence of LDB. Russell bodies within plasma cells, vascular changes, and xanthoma-like hue have been seen in plaques from chronic PKDL. The histopathologic picture in some may also mimic that seen in tuberculoid and lepromatous leprosy, and other granulomatous dermatoses. In contrast to Indian PKDL, epithelioid cell granulomas with giant cells are more common in African PKDL, and vascular changes are rare though neuritis showing LDB has been described.

Introduction

Being an uncommon dermatosis and geographically seen in the eastern region of India, limited reports on histopathology are available about post kala-azar dermal leishmaniasis (PKDL). As the dermatosis has a range of manifestations from the early macules, which progress to form papules, plaques, and nodules, the histopathology varies depending upon the type of lesion biopsied. In case of a polymorphic presentation, the biopsy is best taken from the most indurated lesion, like plaques and papulonodules. However, this opportunity may not be available when the lesions are predominantly macular.

Early and Late Histopathologic Changes

A comprehensive report[1] around the middle of the last century revealed that the infiltrate in PKDL was composed mainly of lymphocytes, macrophages, and plasma cells in varying proportions. The earliest change was noted in the sub-papillary plexus of the macule where histiocytes and lymphocytes were seen, rarely extending to the reticular dermis, and around sebaceous glands and hair follicles in chronic cases; the degree of cellular infiltration increased as the lesions became erythematous and indurated and became densest in the nodular lesions. These changes have been described as three patterns,[2] namely a mild superficial infiltrate seen in macules [Figure 1], dense upper dermal infiltrate in papules, and a diffuse dermal infiltrate in nodules [Figure 2]. A characteristic appearance in nodules is prominent follicular plugging with a dense plasma cell-rich lymphohistiocytic dermal infiltrate that shows an abrupt cut-off in the lower dermis. This appearance is highly suggestive of PKDL even in the absence of Leishman–Donovan bodies (LDB) [Figure 3]. A grenz zone may be seen in a majority of the cases but is absent in the others. Similar observations were made in other studies with an important observation that lymphocytes and plasma cells formed the main component of the infiltrate amidst which were dispersed the macrophages; neutrophils and eosinophils could be seen. Epithelioid cell granulomas are an uncommon finding [Figure 4] and were not observed by some workers[3,4] but were reported in 4 of 88 cases in a large recent series.[2] It was seen in one report[5] that the plasma cells were conspicuous when the infiltrate was mild to moderate in contrast to those with a heavy dermal infiltrate. The density of inflammation was maximal in the superficial dermis as compared to the mid and deep dermis, which showed moderate or sparse inflammation.[6] Large collections of plasma cells showing well-developed Russell bodies can be seen in biopsies of nodules.[7] In a study of 100 cases, edema of the papillary dermis and destruction of the basal cell layer were seen in nodular lesions, whereas hypochromic macules showed decreased melanin in basal cell layer with very little dermal infiltrate.[8] In the infiltrated areas the collagen was thick, hyalinized, seen as broad strands, and slightly basophilic in tinctorial character.[1,4] Vascular changes in the dermis have been observed in chronic lesions. They vary from dilatation and thickening of the blood vessels in early lesions to sclerotic changes around the dermal vessel wall in chronic cases.[2,4] In chronic plaques that have a xanthoma-like hue, fibrosis with venular constriction and subsequent dilatation have been described giving them a deeper orange color.[9] Reports from Africa on PKDL are mostly confined to Sudan. Apart from the main differences summarized in Table 1, in isolated instances psoriasiform hyperplasia of the epidermis, a band like infiltrate similar to lichen planus, and vasculitis have been reported.[10]

Figure 1.

Mild superficial perivascular infiltrate in a macule showing lymphocytes and few plasma cells (inset) (H and E, ×40; inset ×200)

Figure 2.

Dense infiltrate of lymphocytes, histiocytes, and many plasma cells (H and E, ×400)

Figure 3.

Follicular plugging with a dense plasma cell-rich lymphohistiocytic dermal infiltrate that shows an abrupt cut-off in the lower dermis; a clear to less dense subepidermal grenz zone can be appreciated (H and E, ×20)

Figure 4.

Epithelioid cells and giant cells amidst an infiltrate of lymphocytes and plasma cells (H and E, ×200)

Table 1.

Main differences between Indian and African Post kala-azar dermal leishmaniasis

Location	Indian PKDL[1,2,4,11]	African PKDL[12,13,14]
Epidermis	Normal to atrophic or stretched	Hyperkeratosis, parakeratosis, and follicular plugging
	Follicular plugging	Liquefaction degeneration of basal cells with focal infiltration by lymphocytes
Dermis	Lymphocytes and plasma cells predominate with scattered macrophages	Lymphocytes predominate histiocytes are seen but plasma cells are scant or absent
	Generally sparse LDB; numerous may be seen in papules and nodules but almost never in macules	LDB seen in 20% of cases, more so in those extensive involvement (grade 3)
	Epithelioid cell granuloma with or without giant cells rare	In about half the cases scattered epithelioid cells or compact granulomas with giant cells can be seen
	Blood vessels in papulo-nodules show thickened hyalinized walls and endothelial swelling	Neuritis seen with Schwann cell hyperplasia and LDB within nerves
		Blood vessel changes not mentioned
Leishman-Donovan bodies or amastigotes	Maximally found in superficial dermis	Maximally seen just below epidermis
Clinico-pathologic correlation	Changes in blood vessels and collagen were seen in nodules of long duration	No such correlation reported between duration of lesion and histopathology
Electron microscopic findings	Lymphocytes found in intimate contact with melanocytes and basal keratinocytes; dermis infiltrated by a mixture of lymphocytes and macrophages	Rich cellular infiltrate of plasma cells and lymphocytes around parasitized macrophages
Immunopathology	Lymphocytes in early lesions are CD4+ and CD8+, but as PKDL becomes chronic and nodular CD8+cells predominate	Most of the cells are CD3+ with a preponderance of CD4+ over CD8+ cells

The finding that confirms the diagnosis is the demonstration of LDB, which represent the amastigote form of the parasite inside the macrophages or extracellular spaces, seen most prominently immediately beneath the epidermis. The bodies show an increasing gradient from the nearly always negative status in macules to the moderate or heavily parasitized macrophages in the nodules [Figure 5]. Many times this logical conclusion appears too simple and fails to work since the demonstration of LDB is independent of the extent or type of lesion, for no organisms may be demonstrable both in the extensive macular cases[15] and in biopsies from the nodules of PKDL.[4] In the authors' experience LDB are generally sparse and are found after a patient search, though in a minority they may be abundant. Histopathological detection of LDB from macular lesions is very unusual as their numbers are so small.[1,15] In the other types of lesions LD bodies are seen in less than half the number of patients with PKDL.[2,5,16] When numerous, the bodies may at times be confused with histoplasmosis.[17] Roustan et al.[18] and Singh et al.[2] found that the demonstration of organisms was higher from mucosal lesions as compared to cutaneous nodules and recommended biopsying the former if both sites were affected.[2] Special stains like iron hematoxylin[1] or Giemsa do not help much as they do not stain LDB differently from karyorrhectic nuclei.[4] A helpful aid in their differentiation is that nuclear detritus has an intense hematoxyphilic color similar to that of lymphocyte nuclei, whereas LDB are a shade paler.[2]

Figure 5.

Numerous Leishman–Donovan bodies within the macrophage cytoplasm (H and E, ×1000)

Immunohistochemistry

Immunohistochemical techniques using antileishmanial antibodies considerably enhance the demonstration of LDB as compared to hematoxylin and eosin-stained sections in both Indian and Sudanese PKDL,[6,10] particularly in macular forms.[6] The same study[6] showed that the parasite load was highest in the superficial dermis, decreasing in numbers as one reached the deep dermis; more importantly all the nodular lesions studied had a low count of parasites explaining why even slit-skin smears could be negative from nodules. These observations were also made in Sudanese PKDL, a notable finding being that the parasite or parasite antigen could be seen in as high as 88% of cases in immunoperoxidase stained sections compared to 17% with sections stained by hematoxylin and eosin.[12]

Limitations and differential diagnosis

A histopathologic picture mimicking tuberculoid and lepromatous leprosy have been described in PKDL.[2] Unlike the diffuse and scattered infiltrate seen in PKDL, a granuloma composed of epithelioid cells with or without giant cells can be seen; it may be ill formed[19] or compact,[16] often seen in nodules[17] and arranged in zones with the histiocytes and giant cells in the center surrounded by lymphocytes and plasma cells.[1] The granulomatous inflammation may be seen around the nerve twigs[20] confounding the situation further. In PKDL from Sudan, granulomas have been seen more frequently in the papules and nodules and also within the dermal nerve twigs where parasites have also been visualized.[12,13] Thus, even when the clinician has made the diagnosis of PKDL, the pathologist may report it as leprosy in the absence of LDB since both these diseases are usually endemic in the same region and leprosy tends to be commoner and more familiar to the pathologists. Additionally, other granulomatous dermatoses, particularly when the lesions in PKDL are confined to the face, may confound the diagnosis. In these situations molecular tests like PCR may be helpful, failing which a good clinicopathologic correlation must be done[21,22] followed by a response to antileishmanial therapy.

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Conflicts of interest

There are no conflicts of interest.