Leprosy Mailing List, August 29th, 2008
Ref.: Management of nerve abscess
From: Srinivasan H., Chennai, India
Dear Dr Noto,
This is with reference to the query of Dr Ranthilaka Ranawaka regarding management of nerve abscess (LML Aug. 25th, 2008). My views on this topic are as follows.
Nerve abscesses in leprosy are usually ‘cold abscesses’ like tubercular cold abscesses. They occur due to caseation followed by colliquative necrosis tuberculoid granuloma in nerve fibres. They are commonly seen in major nerve trunks and cutaneous nerves of persons suffering from tuberculoid types of leprosy. In major nerve trunks the abscess may be truly intraneural due to necrosis of a nerve fascicle (or even a part of a fascicle) within the nerve, with the ‘pus’ collected inside the nerve, or, the pus may track through the epineurium and come out as a collar stud abscess to form a ‘para-neural’ abscess. Sometimes, a nerve bundle in the outer sheath of the nerve is the site of abscess formation and the abscess remains ‘para-neural’ from the beginning. Occasionally, a lymph node adherent to the nerve sheath (e.g., epitrochlear node adherent to the ulnar nerve) develops caseous necrosis in tuberculoid leprosy and forms a para-neural abscess, clinically indistinguishable from a true nerve abscess tracking from inside the nerve.
The size of the abscess ranges from very small (minute micro abscesses) to very large ‘giant’ abscesses, many centimetres long and wide. The presence of the abscess or it growing in size does not indicate disease activity. Left alone, smaller abscesses tend to subside on their own while larger abscesses often do not do so. They may even keep increasing in size.
There are two concerns associated with the nerve abscesses: i) the abscess per se and ii) the effect of the abscess on the function of the affected nerve trunk.
i.)Unlike acute inflammatory ‘hot’ abscesses, cold abscesses are relatively painless or there maybe only mild nerve pain. So pain is not a major consideration in the management of nerve abscesses. Nor is “disease activity” a concern and that is determined based on other parameters and not on the presence or changes in the size of the abscess. A very large abscess is a cosmetic concern. A visible abscess may also be an embarrassment because it invites the curiosity of neighbours as to its cause (with may be serious social consequences).
ii.)The size of the abscess does not indicate the extent of nerve damage caused by it and the resulting nerve function deficit (NFD). Even a small intra neural abscess can be associated with significant NFD, as the abscess may press on the surrounding fascicles and strangulate them (especially when the epineurium is thickened and fibrosed and does not allow expansion) because of increased intra neural tension. This causes conduction blockage (neurapraxia) in even undamaged nerve fascicles and NFD. This danger does not exist when the abscess breaks through the epineurium (with relief of intraneural hypertension) and becomes para-neural. When the abscess is para-neural from the beginning, there is little danger of the abscess giving rise to NFD.
Management of the abscess depends primarily on the state of the nerve affected. The nerve may show, at the time the abscess is noticed or complained of, (a) significant functional deficit by way of anaesthesia in its area of supply and / or paralysis or weakness of the muscles supplied by that nerve, or, (b) no significant functional deficit. When functional deficit is noticed, one should enquire whether is well established (“irrecoverable”) or “recoverable”. If NFD is well established or long standing (like e.g., long ante dating the onset of the abscess, severe muscle atrophy, muscle paralysis of more than six months duration), it may be considered “irrecoverable”. It may also be considered “irrecoverable” if NFD is complete (i.e., complete sensory-motor paralysis with paralysis of all the muscles normally supplied by the nerve in the case of a mixed nerve). When NFD is considered “irrecoverable”, we may ignore this aspect and consider the abscess per se. We can wait and see if it will subside of its own accord in the course of some months. If it does not, and if the patient desires it, it is dealt with surgically. The exception to this advice is when the abscess involves the overlying skin and there is an imminent danger of the abscess bursting through the skin. In that case, the abscess is surgically dealt with straight away.If the NFD is incomplete or recent (some muscles normally supplied by the nerve are not paralysed or acting weakly, muscle atrophy not severe, paralysis/NFD is not long standing – less than six months duration), it may be considered to be “recoverable NFD” and the abscess is surgically dealt with without much delay. When there is no NFD, ascertain by clinical examination whether the abscess is purely intra neural or whether it is a collar stud or a para-neural abscess.When the abscess is identified as an “intraneural abscess” (fusiform swelling of the nerve, abscess part of the nerve and separate from it) it is dealt with surgically without delay.When the abscess is identified as a “collar stud” or a “para-neural abscess” (abscess forming a swelling by the side of and adherent to the nerve), we can wait and see if it will subside of its own accord in the course of some months. If it does not, and if the patient desires it, it is dealt with surgically. The exception to this advice is when the abscess involves the overlying skin and there is an imminent danger of the abscess bursting through the skin. In that case, the abscess is surgically dealt with straight away.The intraneural abscess is evacuated, its walls curetted thoroughly and the necrosed fascicles are excised. The wound is closed without drain. Firm bandaging is done.Para-neural and collar-stud abscesses are excised, in toto if possible. The abscess track into the nerve is traced into the interior of the nerve and the necrosed fascicles are identified to their full extent and excised. The wound is closed without drain. Firm bandaging is done.I hope the above is of some use.