The histopathologic spectrum of erythema induratum of Bazin

Subcutaneous adipose tissue: Implications in dermatological diseases and beyond

Subcutaneous adipose tissue (SAT) is the deepest component of the three-layered cutaneous integument. While mesenteric adipose tissue-based immune processes have gained recognition in the context of the metabolic syndrome, SAT has been traditionally considered primarily for energy storage, with less attention to its immune functions. SAT harbors a reservoir of immune and stromal cells that significantly impact metabolic and immunologic processes not only in the skin, but even on a systemic level. These processes include wound healing, cutaneous and systemic infections, immunometabolic, and autoimmune diseases, inflammatory skin diseases, as well as neoplastic conditions. A better understanding of SAT immune functions in different processes, could open avenues for novel therapeutic interventions. Targeting SAT may not only address SAT-specific diseases but also offer potential treatments for cutaneous or even systemic conditions. This review aims to provide a comprehensive overview on SAT's structure and functions, highlight recent advancements in understanding its role in both homeostatic and pathological conditions within and beyond the skin, and discuss the main questions for future research in the field.

Should antituberculosis treatment be prescribed in erythema induratum? A case-control and incidence correlation study in Taiwan, 2001-2020

BACKGROUND

Erythema induratum (EI) is a tuberculid associated with Mycobacterium tuberculosis infection. Using polymerase chain reaction (PCR), M. tuberculosis has been identified in Taiwan with a high percentage of EI. However, this pathogen is now rarely detected in Taiwan.

OBJECTIVES

To explore the association between EI, the annual incidence of tuberculosis (TB) in Taiwan and treatment outcomes over the last two decades.

METHODS

Patients diagnosed with EI between 2001 and 2020 were enrolled based on histopathology, tissue culture and positive M. tuberculosis PCR tests. Other cases of panniculitis with positive M. tuberculosis PCR results were used as controls. The clinical information of participants was obtained. The results were correlated with the annual incidence of TB and compared between groups.

RESULTS

Fifty-five biopsy specimens from patients with EI met the inclusion criteria; three (5%) had positive M. tuberculosis PCR results. One patient diagnosed with erythema nodosum in the control group had a positive M. tuberculosis PCR (n = 1/27; 4%). There was no significant relationship between M. tuberculosis and EI (odds ratio 1.5, 95% confidence interval -0.964 to 3.964). The correlation between the incidence of M. tuberculosis and the number of EI cases was not statistically significant (r = -0.185, P = 0.45). Only four patients received anti-TB treatment; they all showed clinical improvement without recurrence. One patient with M. tuberculosis PCR-positive EI was not treated with anti-TB therapy; however, the skin lesion improved after 3 months. No other patients in the EI group were diagnosed with M. tuberculosis infection over a follow-up period of 508 person-years.

CONCLUSIONS

Most cases of EI in Taiwan are nodular vasculitis and not tuberculid, owing to well-controlled TB. This condition can be alleviated without anti-TB treatment.

Disseminated tuberculosis presenting as medium-vessel vasculitis in an immunocompromised host

Cutaneous tuberculosis is an uncommon entity with several clinical forms recognized. Histopathologically, most cases are characterized by granulomatous inflammation and caseating necrosis, although less common findings, including vasculitis, have also been described. We report a 55-year-old male with a history of recently diagnosed dermatomyositis receiving immunosuppression with mycophenolate mofetil and prednisone, who developed multifocal soft tissue abscesses and an indurated erythematous plaque on the back. Skin biopsy of the back revealed a necrotizing medium-vessel vasculitis. Mycobacterium tuberculosis was detected in the skin via acid-fast bacilli stain and confirmed by tissue culture and polymerase chain reaction. Cutaneous findings improved rapidly with antituberculosis therapy. This case illustrates an uncommon clinical and histopathologic presentation of disseminated tuberculosis.

Cutaneous tuberculosis in Rio de Janeiro, Brazil: description of a series of 75 cases

BACKGROUND

Brazil is one of the highest tuberculosis (TB) burden countries of the world. Cutaneous tuberculosis (CTB) is a rare form of extrapulmonary manifestation of tuberculosis. This study aimed to describe the clinico-evolutive, laboratory and therapeutic aspects of CTB cases among patients from a cohort with TB in Rio de Janeiro, Brazil.

METHODS

Cases of diagnosed CTB with microbiologic confirmation or clinical response to anti-tuberculous treatment associated with positive smear or histopathological findings between the years 2000 and 2016 were selected.

RESULTS

Seventy-five patients with CTB were included, most were women (58.7%) with a median age of 42 years. CTB diagnosis was based on culture in only 42.7% of the cases. Scrofuloderma represented 50.7% of the cases, followed by erythema induratum of Bazin (EIB) (18.7%), tuberculous gumma (13.3%), lupus vulgaris (8%), TB verrucosa cutis (4%), orificial TB (2.7%) and associated forms (2.7%). Other TB presentations were pulmonary (22.7%), mammary (6.6%) and osteoarticular (4%). All patients who completed the treatment (97.3%) had their lesions healed. Only two patients (2.6%) needed to change the therapy due to adverse reactions. Fifty percent of EIB patients presented recurrence.

CONCLUSIONS

These data highlight the diversity of CTB presentations and the importance of the skin to assist in early identification and treatment of TB. More studies are necessary to improve the knowledge on EIB for a better approach towards these patients, mainly in cases of recurrence.

Successful treatment of erythema induratum with topical application of antituberculous drugs: A case report

RATIONALE

Erythema induratum, a chronic recurrent lobular panniculitis with vasculitis, is strongly associated with Mycobacterium tuberculosis infection. The recommended drugs include isoniazid, rifampicin, and pyrazinamide, which are typically administered in combination (orally or intravenously). Till date, there are no reports about topical application of anti-tuberculous (anti-TB) drugs for treatment of erythema induratum.

PATIENT CONCERNS

Herein, we present the case of a 73-year-old woman with recurrent ulceration, scarring and obvious pain in her lower legs.

DIAGNOSES

She was diagnosed of erythema induratum.

INTERVENTIONS

Topical anti-TB treatment (3.75% isoniazid twice a day) was necessitated by the development of severe gastrointestinal upset and significant reduction in platelets after oral treatment with isoniazid and rifampicin.

OUTCOMES

The skin lesions showed improvement at one month and remitted mostly at two months. After 6 months, the skin lesions have subsided and no obvious side effects were observed.

LESSONS

Our experience may help expand the therapeutic regimens for cutaneous tuberculosis, and provide physicians with alternative options for management of tuberculosis.

Clinical and histopathological features of cutaneous nontuberculous mycobacterial infection: a review of 13 cases

BACKGROUND

The incidence of cutaneous nontuberculous mycobacterial (NTM) infection has increased in recent decades because of widespread use of immunosuppressive therapy and better detection methods. The histopathology of cutaneous NTM infection is not pathognomic and the organisms are slow and difficult to culture, making diagnosis challenging.

METHODS

We reviewed the clinical and histopathological features of 13 cases of cutaneous NTM infection, and performed panmycobacterial polymerase chain reaction (PCR) on the paraffin blocks.

RESULTS

The immunocompetent patients presented with localized lesions on the extremities, whereas the immunocompromised patients presented with disseminated cutaneous lesions. The histopathology in immunocompetent patients was characterized by pseudoepitheliomatous epidermal hyperplasia, intraepithelial abscesses, transepidermal elimination and dermal granulomatous inflammation accompanied by necrosis and suppuration. The immunocompromised patients showed suppurative inflammation with little granuloma formation and numerous acid-fast bacilli. Paraffin block PCR was positive in 4 of 13 cases (31%), whereas culture was positive in 11 of 13 cases (85%).

CONCLUSION

The aforementioned histological features should help in diagnosing cutaneous NTM infection when combined with clinical and microbiological correlation. In our study, we did not find paraffin block PCR to be superior to conventional culture in detecting cutaneous NTM infection.

Panniculitis: A summary

The diagnosis of panniculitis is felt to be a confusing topic by some pathologists. This summarical article presents inflammatory diseases of the subcutis in a systematic fashion, based on whether they are centered on fibrovascular septa or the adipose lobules, and whether morphologic vasculitis is present or not. Septocentric, non-vasculitis disorders include erythema nodosum, panniculitis that follows the use of "biological" therapeutic agents, lipodermatosclerosis, post-irradiation panniculitis, morphea profunda, and necrobiosis lipodica profunda. Polyarteritis nodosa and Behçet's disease are the conditions that are based in the subcutaneous septa with vasculitis. Predominantly-lobular panniculitides with no vasculitis include pancreatogenic panniculitis, the panniculitis of alpha-1-antitrypsin deficiency, panniculitis associated with lupus erythematosus and dermatomyositis, subcutaneous Sweet syndrome, eosinophilic panniculitis, factitial panniculitis, cold panniculitis, panniculitis following injections of corticosteroids, lipomembranous (ischemic) panniculitis; sclerema neonatorum and subcutaneous fat necrosis of the newborn, and Rosai-Dorfman disease of the subcutis. Erythema induratum and infectious panniculitis are vasculitic and lobulocentric conditions. This article reviews the histological features of these diseases.

A Case of Tuberculous Granulomatous Panniculitis without Vasculitis

We report a case of tuberculous granulomatous panniculitis without vasculitis in an 87-year-old female patient with B-cell chronic lymphocytic leukaemia. One month after starting chemotherapy with chlorambucil and prednisone she presented superficial erythematous plaques on the anterior side of the left leg. Three weeks later erythematous painless deep nodules appeared on the left popliteal fossa and on the left thigh. Cutaneous biopsy revealed granulomatous panniculitis without caseation necrosis or vasculitis. Polymerase chain reaction for Mycobacterium tuberculosis revealed positivity in the skin. The final diagnosis was reactivation of latent tuberculosis (TB) induced by deep immunosuppression associated with chemotherapy and haematological disease. Tuberculous granulomatous panniculitis without vasculitis is a rare presentation of cutaneous TB and may be part of the heterogeneous histopathologic spectrum of erythema induratum of Bazin (nodular vasculitis). Our case shows that the diagnosis of cutaneous TB requires the correlation of clinical findings with histopathology and microbiological tests.

Neutrophilic panniculitis: algorithmic approach to a heterogeneous group of disorders

CONTEXT

Neutrophilic panniculitis encompasses an etiologically and morphologically heterogeneous group of disorders. Correct histopathologic diagnosis is important in identifying certain systemic diseases and guiding appropriate treatment.

OBJECTIVE

To review the clinical and histopathologic features of different types of neutrophilic panniculitis, and to provide a diagnostic algorithm for these disorders.

DATA SOURCES

A review of the literature with emphasis on the distinguishing features of different entities was performed.

CONCLUSIONS

Evaluation for neutrophilic panniculitis entails paying close attention to the pattern of inflammation, the type of fat necrosis present, any evidence of vascular damage, and other relevant histopathologic features. An algorithmic approach integrating all histopathologic, clinical, and laboratory findings is required for correct diagnosis.

Secondary Syphilis with Nodular Vasculitis Mimicking Behçet's Disease

Although, erythema nodosum is a common skin manifestation associated with syphilis, nodular vasculitis is a rare feature. Here, we describe a case of a 22-year-old, human immunedeficiency virus negative, non-immunocompromised man who developed recurrent oral and scrotal ulcers with nodular lesions of the lower extremitie. Behçet's disease was initially suspected, however, his serologic test for syphilis was positive, and he was thus diagnosed with secondary syphilis, with a skin biopsy showing nodular vasculitis. The patient was treated with benzathine penicillin, and the skin lesions disappeared after treatment.

Erythema induratum: case series illustrating the utility of the interferon-γ release assay in determining the association with tuberculosis

BACKGROUND

The interferon-γ release assay (IGRA) is a novel method for detecting previous sensitization to tuberculosis (TB). Despite having several advantages over the tuberculin skin test (TST), including higher specificity and no influence from past bacille Calmette-Guérin (BCG) exposure, there are a limited number of reports describing its application in patients with erythema induratum (EI)/nodular vasculitis (NV), which is usually but not always related to TB.

OBJECTIVES

The aim of our case series was to evaluate the usefulness of the IGRA for determining a TB association in patients with EI/NV.

METHODS

Retrospective chart reviews were conducted on four patients diagnosed with EI/NV at our institution in whom an IGRA had been performed.

RESULTS

All four subjects had positive TST results. The IGRA was also positive and therefore supported a link with TB in two cases. One patient responded completely to anti-TB therapy, whereas the second was lost to follow-up. Both cases unrelated to TB, by virtue of negative IGRAs, demonstrated complete response to immunosuppressive therapy (methotrexate), with one individual having failed anti-TB therapy first.

CONCLUSION

Our case series highlights the utility of the IGRA for establishing a TB association in patients with EI/NV. Although limited by a small sample size, we propose adjunctive use of this test at the time of EI/NV diagnosis, especially in the setting of previous BCG exposure, so that management can be tailored according to whether an underlying relationship with TB exists.

Inflammatory nodules of the leg

There is a group of diseases characterized by inflammatory nodules which generally located on the lower leg. They have certain clinical appearances in common, which often makes a differential diagnosis difficult or impossible on clinical grounds alone. There is a great variation in histopathologic appearance, which depends on the duration of the lesions and sites from specimens are obtained for biopsy. Therefore, separating and subclassifying inflammatory nodule lesions of the legs, based on the subtle clinical and histological variation, is not easy. Despite all these difficulties, a specific diagnosis can be made with an adequate clinic-pathologic correlation.

[Medium and large vessel vasculitis]

Vasculitis comprises a broad group of syndromes characterized by inflammation and necrosis on the walls of blood vessels, resulting in narrowing or occlusion of the lumen. The distribution of involved blood vessel varies considerably and serves as the basis for one classification of vasculitic syndromes: large vessels (Takayasu arteritis, giant cell arteritis); medium and small muscular arteries (polyarteritis nodosa, Churg-Strauss syndrome, Wegener's granulomatosis, vasculitis in rheumatic diseases); and small vessels ("hypersensitivity" vasculitis, Henoch-Schonlein purpura, microscopic polyangiitis, cryoglobulinemia). This article reviews medium and large vessel vasculitis and current treatment options; it also presents a comprehensive approach to diagnosing and treating patients with suspected cutaneous vasculitis.

Erythema induratum of Bazin in a child: evidence for a cell-mediated hyper-response to Mycobacterium tuberculosis

Tuberculids are chronic nodular skin eruptions believed to be a systemic reaction to Mycobacterium tuberculosis. We report on a 6-year-old boy with tender subcutaneous lesions on his legs. A tuberculin skin test resulted in 2.5 cm of induration and an interferon-gamma releasing assay was also markedly positive. A diagnosis of erythema induratum of Bazin was confirmed on skin biopsy. The patient was successfully treated with multi-drug antituberculosis therapy.

Subcutaneous inflammation (panniculitis) in tibio-tarsal joint of rats inoculated with complete Freund's adjuvant

Complete Freund's adjuvant (CFA)-induced arthritis in rats, which presents similar features to rheumatoid arthritis, is a model widely used in aetiopathogenetic and investigational drug studies. In this model, arthritis is induced by intradermal injection of Mycobacterium tuberculosis suspended in mineral oil in the hind footpad. Although the histopathology findings in the joint are well described, the marked subcutaneous features of panniculitis that concomitantly occur in this model have received no attention. The objective of this paper is to describe the subcutaneous histopathological features in 8 Wistar rats after intraplantar injection of CFA. We studied the subcutaneous histopathological features in 8 Wistar rats after intraplantar injection of CFA in the left hind paw. The levels of subcutaneous inflammation of the animals in this study were evaluated for the histological characteristics present in the tissue and scored with 4 parameters (acute inflammation, chronic inflammation with fibrosis, subcutaneous and profound soft tissue necrosis, and the presence of giant cells, neutrophils, macrophages and lymphocytes) on days 4, 7, 11 and 15 after induction. All animals developed intense subcutaneous inflammation characteristic of panniculitis, with predominance of acute changes in the initial period, with progression to a self-perpetuating chronic fibrotic process on day 15. These observations precede the joint changes. Besides being an interesting model for better studying diseases with panniculitis, our observations bring up issues concerning the possible relations between subcutaneous and joint inflammatory changes.

Nephrogenic systemic fibrosis with septal panniculitis mimicking erythema nodosum

Nephrogenic systemic fibrosis/nephrogenic fibrosing dermopathy is an idiopathic fibrosing disorder recently described in patients with renal disease. The typical histology in nephrogenic systemic fibrosis consists of haphazardly arranged dermal collagen bundles with clefting, collagenous change which extends into the subcutaneous septa, mucin deposition, fibroblast proliferation, and increased elastic fibers with minimal inflammation. We present a 65-year-old female with classic clinical features whose biopsy demonstrated unique histologic features of septal pannicilitis with lymphocytic aggregates and Miescher's radial granulomas mimicking erythema nodosum.

Cutaneous Vasculitis Update: Neutrophilic Muscular Vessel and Eosinophilic, Granulomatous, and Lymphocytic Vasculitis Syndromes

Most biopsies of cutaneous vasculitis will exhibit a small vessel neutrophilic vasculitis [leukocytoclastic vasculitis (LCV)] that is associated with immune complexes on direct immunofluorescence examination or, less commonly, antineutrophilic cytoplasmic antibodies (ANCA) by indirect immunofluorescence testing. Is in uncommon for skin biopsy to reveal solely a neutrophilic arteritis signifying the presence of cutaneous polyarteritis nodosa or, if accompanied by significant lobular panniculitis, nodular vasculitis/erythema induratum. In other cases, cutaneous vascular damage (fibrinoid necrosis, muscular vessel wall disruption, or endarteritis obliterans) will be mediated by a nonneutrophilic inflammatory infiltrate. Eosinophilic vasculitis can be a primary (idiopathic) process that overlaps with hypereosinophilic syndrome, or it can be a secondary vasculitis associated with connective tissue disease or parasite infestation. Authentic cutaneous granulomatous vasculitis (versus vasculitis with extravascular granulomas) can represent a cutaneous manifestation of giant cell arteritis, an eruption secondary to systemic disease such as Crohn's disease or sarcoidosis, or a localized disorder, often a post-herpes zoster (HZ) phenomenon. Lymphocytic vasculitis is a histologic reaction pattern that correlates with broad clinical differential diagnosis, which includes connective tissue disease - mostly systemic lupus erythematosus (SLE), endothelial infection by Rickettsia and viruses, idiopathic lichenoid dermatoses such as perniosis or ulcerative necrotic Mucha-Habermann disease, and angiocentric cutaneous T-cell lymphomas. Skin biopsy extending into the subcutis, identifying the dominant inflammatory cell and caliber of vessels affected, extravascular histologic clues such as presence of lichenoid dermatitis or panniculitis, and correlation with clinical data allows for accurate diagnosis of these uncommon vasculitic entities.

Histopathologic spectrum of erythema nodosum

Erythema nodosum (EN) is the most common panniculitis and histologically represents the prototype of a septal panniculitis. However, the histologic findings can be quite variable. We describe four patients with EN who each underwent two consecutive biopsies. In each case, the first biopsy showed histopathologic features that fall outside the usual spectrum of disease. Two cases showed predominantly neutrophilic infiltrates with focal suppuration as well as vasculitis of medium-sized arteries. The areas of suppuration were more extensive in the first case prompting special stains for microorganisms that were all negative. The third case demonstrated a lobular panniculitis with a predominantly lymphohistiocytic infiltrate. Special stains were negative in this case as well. The fourth case revealed vasculitis of a medium sized artery, small vessel vasculitis, and a mixed septal and lobular panniculitis with a polyclonal population of atypical lymphocytes. In all patients, the clinical course and the subsequent biopsy were classic for EN. We conclude that lobular neutrophilic panniculitis with suppuration, small vessel vasculitis, and even medium vessel arteritis may rarely occur in EN. There are few clues in these unusual cases that allow for a specific diagnosis from the start, and often, a second biopsy is required.

Mycobacteria other than Mycobacterium tuberculosis are not present in erythema induratum/nodular vasculitis: a case series and literature review of the clinical and histologic findings

Erythema induratum (EI)/nodular vasculitis (NV) is characterized by recurrent crops of tender oedematous nodules on the lower legs. A lobular panniculitis with granulomatous inflammation, vasculitis, focal necrosis and septal fibrosis is present. Mycobacterium tuberculosis DNA has been detected in some lesions by means of polymerase chain reaction (PCR). Ten cases of EI/NV were found. H&E slides were reviewed. PCR assays for M. tuberculosis and mycobacteria other than M. tuberculosis (MOTT) were performed. PCR did not reveal M. tuberculosis (0%) or MOTT (0%) DNA, with positive controls, indicating the reliability of the assays. Among the MOTT, cutaneous infections are most commonly caused by M. marinum. Subcutaneous tuberculoid granulomas may be seen with M. kansasii, M. marinum, M. scrofulaceum and M. avium complex. M. gordonae, M. szulgai and M. malmoense rarely cause cutaneous infections. M. simiae, M. gastri and M. asiaticum are probably not cutaneous pathogens. M. tuberculosis and MOTT DNA was not found in EI/NV. EI/NV has diverse aetiologies with varying pathogeneses leading to similar histologic changes. The cases analysed may not have had an infectious aetiology. However, in EI/NV, performance of PCR for MOTT as well as M. tuberculosis complex may still be beneficial, particularly in cases from immunocompromised hosts.

Erythema induratum of Bazin and renal tuberculosis: report of an association

Erythema induratum of Bazin is a disease that usually affects women, in whom erythematous subcutaneous nodules and plaques appear on the posterior part of the lower extremities, some of which ulcerate. In many countries, tuberculosis is still the main etiologic factor. We report a case of a 40-year-old woman who presented a course of protracted and recurrent episodes over five years of cutaneous lesions on her legs. These tend to involute, but new crops appear at irregular intervals. It was painful, erythematous-violaceous nodules, some of which drained a reddish secretion. The histopathologic features of the lesions demonstrated inflammatory infiltration, with predominance of neutrophils in dermis and hypodermis, necrotizing vasculitis in the arterioles and septal fibrosis. There was no granuloma. The Ziehl-Neelsen stain did not revealed acid-fast bacilli, and the culture of biopsy specimen was negative. The tuberculin skin test was strongly positive (17 mm). The chest X-ray was normal. Few months later she presented adynamia and urinary complaints, such as polacyuria and dysuria. It has been done an urynalysis, which demonstrated acid pH urine, sterile pyuria and microscopic hematuria. It was then raised the diagnostic hypothesis of renal tuberculosis. The urine culture for M. tuberculosis was positive in two out of ten samples. The treatment was instituted with rifampin, isoniazid and pyrazinamide, with complete regression. This case illustrates a clear association between erythema induratum and renal tuberculosis, demonstrated by the remission of the cutaneous lesions after the treatment of the renal tuberculosis.

Panniculitis. Part II. Mostly lobular panniculitis

The second part of our review of panniculitis summarizes the clinicopathologic features of the mostly lobular panniculitides. Erythema induratum of Bazin (nodular vasculitis) represents the most common variant of lobular panniculitis with vasculitis, although controversy persists about the nature of the involved vessels. Mostly lobular panniculitides without vasculitis comprise a series of disparate disorders. These include sclerosing panniculitis that results from chronic venous insufficiency of the lower extremities; panniculitis with calcification of the vessel walls such as calciphylaxis and oxalosis; and inflammatory diseases with crystals within the adipocytes such as sclerema neonatorum, subcutaneous fat necrosis of the newborn, and poststeroid panniculitis. Connective tissue diseases, such as systemic lupus erythematosus and dermatomyositis, pancreatic diseases, and alpha(1)-antitrypsin deficiency may also show a mostly lobular panniculitis with characteristic histopathologic features. Lobular panniculitis may also be an expression of infections, trauma, or factitial causes involving the subcutaneous fat. Lipoatrophy refers to a loss of subcutaneous fat due to a previous inflammatory process involving the subcutis, and it may be the late-stage lesion of several types of panniculitis. In contrast, lipodystrophy means an absence of subcutaneous fat with no evidence of inflammation and often the process is associated with endocrinologic, metabolic, or autoimmune diseases. Finally, cytophagic histiocytic panniculitis is the term that has been used to describe two different processes: one is inflammatory, a lobular panniculitis, and the other one is neoplastic, a subcutaneous T-cell lymphoma. The only common feature of these two different processes is the presence of cytophagocytosis in the lesions. (J Am Acad Dermatol 2001;45:325-61.)

LEARNING OBJECTIVE

At the completion of this learning activity, participants should be familiar with the pathogenesis, clinical manifestations, histopathologic findings, and treatment options for the most frequent variants of the lobular panniculitides.

Nodular tuberculid: a report of four patients

The tuberculids are hypersensitivity reactions to Mycobacterium tuberculosis (MTB) and include papulonecrotic tuberculid (PNT), lichen scrofulosorum, erythema induratum of Bazin (EIB), and phlebitic tuberculid. Papulonecrotic tuberculid displays papulonecrotic lesions mostly on the extensor surfaces of the limbs. Histopathology shows necrosis, granulomatous inflammation (GI), and occasionally vasculitis, usually in the superficial dermis. Erythema induratum of Bazin shows nodulo-ulcerative lesions on the posterior aspect of the legs. Histopathology reveals a septolobular panniculitis, necrosis, GI, and vasculitis. The Mantoux test is strongly positive and associated tuberculosis (TB) may be present in both conditions. MTB cannot be demonstrated with a Ziehl-Neelsen (ZN) stain or cultured. The polymerase chain reaction has demonstrated MTB DNA in PNT (50%) and EIB (25%). The tuberculids respond to full anti-TB treatment. We document four patients with nodules on the legs in whom the pathologic changes were situated in the deep dermis and adjacent subcutaneous fat. Nodular tuberculid (NT) is regarded as a suitable term for these lesions. All patients were female. Their ages were 19 months, 12 years, 17 years, and 5 years. All patients presented with nodules on the limbs. These nodules were approximately 1 cm in diameter, dull red or bluish-red, and nontender. Ulceration was not present. The number of nodules varied from a few to many. The Mantoux test was strongly positive in all the patients. Associated pulmonary TB was present in two patients. Histopathology showed GI (n = 4), vasculitis (n = 2), and coagulative necrosis (n = 2). A ZN stain was negative in each case. All patients received anti-TB treatment for 6 months [rifampicin (n = 4), isoniazid (n = 4), pyrazinamide (n = 4), and ethambutol (n = 2)]. At 12 months follow-up, skin and pulmonary lesions had resolved in all. Nodular tuberculid should be distinguished from arthropod bites and papular urticaria, dermal erythema multiforme, evolving vasculitis, evolving folliculitis, and erythema nodosum. Histopathologically NT should be distinguished from other causes of granulomatous vasculitis and GI with or without necrosis. In children with nodules on the limbs unresponsive to routine treatment, skin biopsy should be done to exclude NT. Nodular tuberculid represents a hybrid between PNT and EIB with characteristic clinicopathologic features and should be included in the classification of cutaneous TB.

Diagnosis: erythema nodosum or not?

Erythema nodosum is the final common pathway to a myriad of insults and is thought to be a hypersensitivity reaction centered in the subcutis. To recognize the histological spectrum of erythema nodosum, one must be aware of the morphologic chronology of the disease (early, fully developed, late) and its clinical variants (erythema nodosum migrans). This article reviews the range of changes that can be seen in this prototype of a septal panniculitis and describes the diversity that may be accepted in the diagnosis. Differential diagnoses at each stage of disease development are discussed. The criteria elaborated should assist the pathologist in answering the clinician's query, "Erythema nodosum, or not?"