Ultrasonography of the swelling was performed using a 7.5-MHz
transducer. A well-defined elliptical lesion was seen on the
lateral aspect of the leg just below the knee joint. The central
portion of this lesion was clearly anechoic, whereas the walls were
thickened, irregular, and echogenic (Figures 1 and 2). On the basis
of the finding of a tubular, linear lesion along the course of a
nerve, the differential diagnosis included organized hematoma,
abscess, or mass/tumor. With the clinical picture, a diagnosis of
leprotic nerve abscess was made.
At surgery, this swelling was identified as an enlarged lateral
popliteal nerve. On incision, the walls of the abscess were thick
and irregular, and dirty yellow pus was drained. The pus smear was
positive for Mycobacterium leprae.
Bacterial parasitization of peripheral nerves is a unique feature
that is characteristic of leprosy. In most instances, the resulting
neural lesion remains as a granuloma, but in a few cases the
granuloma may soften and develop into an "abscess." Progression to
abscess formation is most commonly seen in patients with
tuberculoid leprosy. Rarely, however, nerve abscess may also
develop in other types of leprosy.1
Mycobacterium leprae has a predilection for peripheral
nerves. The bacterial dissemination may be hematogenous or by
contiguous spread from skin. The usual habitat in the nerve is the
Schwann cell but occasionally the ensheathed axon becomes involved.
The Schwann cells assume a phagocytic function and evolve into
macrophages or epitheloid cells, resulting in the formation of a
granuloma. Invasion of the endoneurium may follow, and the whole
endoneurial zone may appear to be occupied by epitheloid cells with
or without the presence of bacilli. Caseation may occur in
microscopic foci within the granulomas, or areas of necrosis may
coalesce, forming a cold abscess, particularly when the immunity is
high. Cold abscesses occur more frequently in the tuberculoid form,
especially in India.2,3
High-resolution ultrasound can effectively assess the
preoperative 3-dimensional localization and the internal
echotexture of masses arising from peripheral nerves.
High-resolution sonography has identified normal peripheral nerves,
all having echogenic fibrillar echotexture. A tubular/linear
hypoechoic lesion along the course of a nerve should suggest an
organized hematoma, an abscess, or a mass/tumor. In the appropriate
clinical settings, a diagnosis of nerve abscess can be considered.
In this case, the central anechoic area was frank pus, which was
positive for lepra bacilli, surrounded by a thickened nerve sheath.
This appearance may be typical of a cold abscess of a superficial
nerve in leprosy.4
Once the nerve abscess has been detected, it has to be incised
and drained; otherwise, it may rupture through skin onto the skin's
surface. Surgical incision and drainage without disturbing the
intact nerve fibers is the method of choice. It has been suggested
that an operation must be undertaken to rid the patient of the
deleterious complications that may result because of persistent
pressure on the nerve fibers that is caused by the tension within
the nerve sheath.5,6
The case reported here illustrates the sonographic appearance
and management of nerve abscess, a rare complication exclusive to
leprosy. Leprotic nerve abscess is an extremely rare manifestation
of leprosy. However, in the appropriate clinical settings and with
the characteristic sonographic appearance, a diagnosis of nerve
abscess should be considered, especially in endemic areas.
- Kumar P, Saxena R, Mohan L, et al. Peripheral nerve abscess in
leprosy: Report of twenty cases. Indian J
- Char G, Cross JN. Ulnar nerve abscess in Hansen's disease. West
Indian Med J. 1986; 35(1):66-68.
- Singh G, Ojha D. Leprotic nerve abscesses. Dermatologica.1969;
- Taneja K, Sethi A, Shiv VK, et al. Diagnosis of nerve abscess
in leprosy by sonography.Indian J Lepr.1992;64:105-107.
- Sehgal VN, Tuli SM. Leprotic nerve abscess: A case report.
IndianJ Dermatol. 1967;13(1):19-20.
- Browne SG. Leprous nerve abscess: Report of two cases. Lepr