-Dr Sowmya Srinivas

INTRODUCTION  When circulating blood reaches the capillaries, part of its fluid content passes into the surrounding tissues as tissue fluid.  Most of this fluid re-enters the capillaries at their venous ends.  Some of it is, however, returned to the circulation through a separate system of lymphatic vessels (usually called lymphatics).  The fluid passing through the lymphatic vessels is called lymph.  The largest lymphatic vessel in the body is the thoracic duct.  The thoracic duct ends by joining the left subclavian vein at its junction with the internal jugular vein.  On the right side there is the right lymphatic duct that has a similar termination.

 Scattered along the course of lymphatic vessels there are numerous small bean- shaped structures called lymph nodes that are usually present in groups.  As a rule lymph from any part of the body passes through one or more lymph nodes before entering the blood stream.  Lymph nodes act as filters removing bacteria and other particulate matter from lymph.  Lymphocytes are added to lymph in these nodes.

NORMAL HISTOLOGY  The lymph node has an outer zone that contains densely packed lymphocytes, and therefore stains darkly: this part is the cortex.  Surrounded by the cortex, there is a lighter staining zone in which lymphocytes are fewer: this area is the medulla.  Within the cortex there are several rounded areas that are called lymphatic follicles or lymphatic nodules.  Each follicle has a paler staining germinal centre surrounded by a zone of densely packed lymphocytes.

TB LYMPH NODE  Its the most frequent presentation of extrapulmonary tuberculosis, usually occurring in the cervical region (“scrofula”).  In HIV-negative individuals, lymphadenitis tends to be unifocal and localized.  HIV-positive people, on the other hand, almost always have multifocal disease, systemic symptoms, and either pulmonary or other organ involvement by active tuberculosis.

GROSS FEATURES  Large multinodular mass that resembles carcinoma with multiple foci of caseous necrosis.

TUBERCULOUS LYMPHADENITIS  Its a chronic specific granulomatous inflammation with caseation necrosis.  The characteristic morphological element is the tuberculous granuloma (caseating tubercule) : giant multinucleated cells (Langhans cells), surrounded by epithelioid cells aggregates, T cell lymphocytes and few fibroblasts.  Granulomatous tubercules evolve to central caseous necrosis and tend to become confluent, replacing the lymphoid tissue.

TUBERCULOUS GRANULOMA  Multinucleated giant cell : microns, numerous small nuclei (over 20) disposed at the periphery of the cell (crown or horseshoe), abundant eosinophilic cytoplasm.  Epithelioid cells are activated macrophages resembling epithelial cells : elongated, with finely granular, pale eosinophilic (pink) cytoplasm and central, ovoid nucleus.  At the periphery are the lymphocytes (T cells) and rare plasma cells and fibroblasts.  Caseous necrosis is a central area, amorphous, finely granular, eosinophilic (pink).

LEPROSY  Leprosy (lepra) is a chronic infection caused by Mycobacterium leprae. It affects mainly the skin, nasal mucosa, and peripheral nerves.  Mycobacterium leprae is an obligate, intracellular, gram-positive organism that is also acid fast, although less so than M. tuberculosis.  Mycobacterium leprae is found predominantly in three main cell types in the skin: Schwann cells, endothelial/perithelial cells, and cells of the monocyte-macrophage system

RIDLEY–JOPLING CLASSIFICATION  Tuberculoid Leprosy (TT)  Borderline-tuberculoid (BT)  Borderline (BB)  Borderline-lepromatous (BL)  Lepromatous Leprosy (LL)

SIGNS AND SYMPTOMS  Its a systemic disease, although the primary clinical manifestations are in the skin.  Mucosal involvement may lead to ulceration of the nasal septum.  Nerve lesions may result in acral anaesthesia, claw hand, and foot drop.  The cutaneous lesions, which are usually symmetrical, include multiple small macules, infiltrated plaques, and nodules with poorly defined borders.

MICROSCOPY Tuberculoid leprosy:  Epithelioid histiocytes surround small cutaneous nerves  Langerhans giant cells may be seen but without necrosis.  Bacilli are usually scarce

LEPROMATOUS LEPROSY  Has collections and sheets of heavily parasitized macrophages within the dermis, with a sparse sprinkling of lymphocytes  Rarely, subcutaneous and deep dermal inflammatory nodules are present.  In older lesions, the macrophages have a foamy appearance (lepra cells, Virchow cells).  Numerous acid-fast bacilli are present in macrophages, sweat glands, nerves, Schwann cells, and vascular endothelium.

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