Introduction/Clinical Features/Pathogenesis
Erythema induratum is the prototypic lobular panniculitis. Another term for it is Bazin's disease,
recognizing Dr. Bazin who first described the entity in 1861. This unique form of panniculitis is thought
to be related to tuberculosis infection at a distant site; many cases have been shown to be in the setting
of concurrent or antecedent tuberculosis infection of the lung, lymph nodes or bones, while M.tuberculosis
genome has been demonstrated in lesions of erythema induratum. Further proof that these lesions are
intimately related to tuberculosis infection and, represent a tuberculid (ie an id reaction to non-viable
M.tuberculosis antigens is the rapid response of lesions to antituberculous therapy. Clinically, the
lesions present as dusky bluish nodules with variable ulceration involving the posterior calves of typically
obese, elderly females. There may be an exacerbation of these lesions with cold exposure and in fact, some
patients may have concomitant lesions of perniosis.
Histopathology
The histopathology mirrors the morphology of primary tuberculosis. Within the lobule of the fat, there are
discrete zones of fibrinoid necrobiosis within which an admixture of inflammatory debris is noted, and there
is an accompanying palisading infiltrate composed of mononuclear and multinucleated histiocytes, the latter
of Langhans' type.
There may be permeation of the interstitium by a neutrophilic dominant infiltrate imparting a suppurative,
necrotizing granulomatous morphology to this inflammatory subcuticular reaction. Vasculitis may affect the
interstitial vessels of the fat lobule; this vasculitis may have a granulomatous morphology, but more often,
capillaries of the interstitial spaces of the fat lobule are occluded by fibrin thrombi and do not have an
accompanying inflammatory cell reaction, hence defining a pauci-inflammatory thrombotic micro-angiopathy.
This thrombotic micro-angiopathy may be important pathiophysiologically, identifying those patients who are
predisposed to developing erythema induratum in the setting of distant tuberculosis infection. It is
possible that patients who have underlying pro-coagulant and/or hyperviscosity states may be predisposed to
preferential trapping of immune complexes in their subcutaneous vasculature, leading to the propagation of
an inflammatory response to trapped non-viable microbial antigen complex with immunoglobulin.
A recent study reviewed the histomorphologic spectrum encountered in this uncommon form of panniculitis.The
classic histology described a necrotizing vasculitis in concert with caseating granulomas in a predominantly
lobular distribution. In this review they indicated that the spectrum of inflammatory changes could be
broader. Specifically while all cases showed some degree of neutrophilic vascular inflammation and
necrosis, the inflammatory cell infiltrate could be predominantly neutrophilic rather than being either
granulomatous or granulomatous and suppurative in nature. Furthremore the inflammation could be very focal
being centered primarily around a single vessel; such cases may be appropriately categorized as "nodular
vasculitis".
Differential Diagnosis
The main differential diagnosis is with the entity of nodular vasculitis. We feel that nodular vasculitis
is closely related to erythema induratum, however, it is a suppurative lobular panniculitis without a
concomitant granulomatous component and while infection is a probably trigger, the microbial antigen is
typically a bacterial form that can evoke a suppurative diathesis, and not one of Mycobacterial derivation.
As with erythema induratum, a thrombotic microangiopathy within the interstitial of the fat lobule is highly
characteristic. Any case of suppurative and granulomatous panniculitis must be evaluated for being a
primary effective focus as certain hematogenously-disseminated infections, such as cryptococcus or other
deep mycotic infections can manifest as a primary inflammatory process within the subcutaneous fat. Hence,
all such cases should have special stains performed for exclusion of an active infection.
Pathogenesis
The role of mycobaterial antigen in propagating these lesions has been demonstrated through polymerase chain
reaction assays which have documented a 123 base pair sequence of IS61110 insertion sequence of the
Mycobacterium complex in lesional skin of patients with erythema induratum. In this study those cases which
were positive showed the greatest degreee of tissue necrosis. There was no further correlation with respect
to clinical features or the presence of vasculitis and granulomatous inflammation.
References
- Baselga E, Margall N, Barnadas MA, Coll P, de Moragas JM. Detection of Mycobacterium tuberculosis DNA in
lobular granulomatous panniculitis (erythema induratum-nodular vasculitis). Arch Dermatol 1997;133:532-3
- Hood AF, Kwan TH, Mihm MC Jr, Horn TD. Primer of Dermatopathology. 2nd edition. Boston: Little, Brown &
Co, 1993
- Reed RJ, Clark WH, Mihm MC Jr. Disorders of the panniculus adiposus. Hum Pathol 1973;4:219-30
- Schneider JW, Jordan HF The histopathologic spectrum of erythema induratum of Bazin. Am J Dermatopathol
1997;19:323-33
- Yen A, Fearneyhough P, Rady P, Tyring S, Diven D. Erythema induratum of Bazin as a tuberculid: Confirmation
of Mycobacterium tuberculosis DNA polymerase chain reaction analysis. J Am Acad Dermatol 1997;36:99-101
