Surgical treatment of a tomaculous neuropathy

T.F. TAGGART and T.R. ALLEN

Orthopaedic Department, Chesterfield and North Derbyshire Royal Infirmary, Chesterfield UK

Case History

Discussion

 

 

References

Compressive neuropathy of the ulnar nerve at the elbow is the second most common nerve entrapment in the upper limb. Eight possible anatomical points of constriction have been identified. The most common constriction being the intermuscular septum proximally or between the two heads of the flexor carpi ulnaris in the cubital canal distally. Surgical release is successful in 80-90% of cases. Certain rare genetic conditions can predispose susceptible peripheral nerves to similar compressive neuropathies but there is no literature on surgical treatment of such patients. We present a case of hereditary neuropathy with liability to pressure palsy (HNPP) often known as ‘tomaculous’ neuropathy, in a patient with ulnar nerve symptoms who underwent a surgical release.

Key words: Neuropathy, pressure palsy, tomaculous

J.R.Coll.Surg.Edinb., 46, August 2001, 240-241

CASE HISTORY

A 28-year-old right-handed welder presented with an 8-month history of sensory changes, discomfort with prolonged grip and difficulty moving small objects (keys and coins) in his right hand. This was affecting his ability to undertake his job effectively. He had no history of injury to the right wrist or elbow in the past, and did not complain of any neck trouble. The family history revealed that one other sibling, and also his mother, suffered with bilateral carpal tunnel syndrome.

On examination, no muscle wasting or trophic changes were observed. There was a full range of symmetrical movements in both limbs. There was acute tenderness over the ulnar nerve at the elbow and Tinel’s sign was positive. There was reduced perception of fine touch (using Semmes-Weinstein monofilaments) and reduced Weber two point discrimination, affecting the whole of the little and the ulnar side of the ring finger. Froment’s test was negative. Power grip was 80 kg force on the right and 70 kg on the left (using the Jamar grip dynamometer). Carpal tunnel syndrome tests were negative.

At this point a diagnosis of right ulnar neuritis was made, and he was sent for nerve conduction studies.

Sensory studies of both median and ulnar nerves and the right sural nerve revealed sensory action potentials with reduced amplitudes and reduced sensory conduction velocities.

Motor studies of the right ulna nerve showed conduction block at the level of the elbow and reduction of motor conduction velocity across the elbow. A motor study of the left ulnar nerve revealed a reduction in the motor conduction velocity across the elbow. Distal motor latencies to the right and left abductor policis brevis were prolonged. The distal motor latency to the right extensor digitorum brevis was prolonged and the motor conduction velocity of the right peroneal nerve was slightly reduced.

These findings suggested a moderately severe, sensori-motor, right ulnar nerve lesion at the level of the elbow. There was also sub-clinical bilateral carpal tunnel syndrome and a left ulnar nerve lesion at the level of the elbow. In addition, there was evidence of a background generalised neuropathy. The findings were strongly suggestive of a tomaculous neuropathy.

After discussion with a neurologist it was agreed to proceed with a surgical release without transposition of the right ulnar nerve. At operation, the utmost care was taken to protect pressure areas, no tourniquet was used. The soft tissues were released with great care so as to not traumatise the ulnar nerve. The intermuscular septum and the cubital canal were grossly normal. The nerve was also macroscopically normal. The patient made a good post-operative recovery and, 6 months post-operatively there are no residual neurological symptoms in his right arm.

DISCUSSION

Hereditary neuropathy with liability to pressure palsy (HNPP) is an autosomally dominant transmitted disease, first described by De Jong in 1947, which gives rise to foci of peripheral nerve hypermyelination, reducing conduction and leading to episodes of palsy and sensory changes that are linked to sensitivity to pressure and traction on the affected nerve roots. The age of onset is most commonly at 20-45 years, but symptoms have been reported as early as age 4 (Roose and Thygesen, 1972), and as late as age 67 years (Staal et al, 1965). 1,2 The most commonly affected nerves are the ulnar, radial, medial and common peroneal nerves. The disease can also affect the musculo-cutaneous, axillary, long thoracic, supra-scapular, femoral or sciatic nerves.5 Rarely, cranial nerves are affected. Only recently the cause has been identified as a molecular level: a submicroscopic deletion of the 17P.11.2 chromosome, exactly the same region that the ulnar, radial, medial and common peroneal nerves. The disease can also affect the musculo-cutaneous, axillary, long thoracic, supra-scapular, femoral or sciatic nerves.3 Rarely, cranial nerves are affected. Only recently the cause has been identified at the molecular level: a submicroscopic deletion of the 17P.11.2 chromosome, exactly the same region that chromosome duplication occurs in Charcot Marie Tooth disease, type 1A.4 This gene locus (PMP22) controls the production of peripheral myelin protein, essential in the healthy peripheral nerve myelination and ultimate smooth function of the peripheral nerve.

The word tomaculous (tomaculum = Latin for sausage) was the description given by Madrid and Bradley (1975) to the areas of microscopic hypermyelination on individual nerve fibres from sural nerve biopsies of affected patients.3 Other microscopic findings were thinly myelinated axons, supernumerary Schwann cells forming ‘onion bulbs’, which are identifying fingerprints of repeated re-myelination and demyelination.

Electron-microscopy suggests that tomaculae are unstable structures and are prone to degeneration.5 Similar findings have been identified in patients with rare inherited metabolic disorders including amyloidosis and mucupolysaccharidoses.6 Only recently, has it been possible to diagnose HNPP more rapidly and economically using polymerase chain reaction technology on nerve biopsies rather than nerve conduction studies and eletron microscopy alone.7

For the majority of patients, the onset of symptoms can be linked with an episode of minor trauma but, quite often, they are spontaneous and unexplained. The natural cause of the disease can vary from symptoms that disappear within weeks, sometimes months, to those that exhibit chronic persistent neurological symptoms.8 Clearly, patients with symptoms that resolve fairly rapidly are unlikely to benefit from surgical intervention, but the group of patients with persistent symptoms, as in the patient we have presented, may well benefit from decompression of the affected nerves.

REFERENCES

1. Roos D, Thygesen P. Familial recurrent polyneuropathy. A family and a survey. Brain 1972; 95:235-48
2. Staal A, de Weerdt CJ, Went LN. Hereditary compression syndrome of peripheral nerves. Neurology 1965; 15: 1008-17
3. Madrid R, Bradley WG. The pathology of neuropathies with a focal thickening of the myelin sheath (tomaculous neuropathy). J Neurol Sci 1975; 25:415-48
4. Debruyne J, Dehaene L and Martin JJ. Hereditary pressure-sensitive neuropathy. J Neurol Sci 1980; 47: 385-94
5. Adkofer K, Frei R, Neuberg DH, Zielasek J, Toyka KV, Suter U. Heterozygous peripheral myelin protein 22 deficient mice are affected by a progressive demyelinating tomaculous neuropathy. J Neurosci 1977; 17:4662-71
6. Karpati G, Carpenter S, Eisen AA, Wolfe LS, Feindel W. Multiple peripheral nerve entrapments. Arch Neurol 1974; 31: 418
7. Beckman A, Schroder JM. Screening for Charcot-Marie-Tooth type 1A and hereditary neuropathy with liability to pressure palsy in archival nerve biopsy samples by direct-double-differential PCR. Acta Neuropathologica 2000; 100: 494-8
8. Earl CJ, Fullerton PM, Wakefield GS, Schutta HS. Hereditary neuropathy with liability to pressure palsies. Q J Med. New series XXXIII. 1964; 132:481-98

Copyright date: 12th June 2001
Correspondence: Mr TF Taggart, Market Cottage, Main Street, Winster, Matlock DE4 2DJ, UK

2001 The Royal College of Surgeons of Edinburgh, J.R.Coll.Surg.Edinb.