Ulnar Neuropathy Caused by Intraneural Cold Abscess due to Leprosy: Case Report

Ulnar neuropathy due to cubital tunnel syndrome is a common presentation in elective orthopaedic clinics with causes usually attributed to idiopathic chronic compression. However, rare diagnoses should be considered. We present a case of chronic insidious ulnar neuropathy in a 52-year-old female with a 2-year history of progressive left hand weakness and decreased sensation. She was born in West Africa and she was noted to be generally fit and healthy. Surgical exploration and decompression of ulnar nerve showed fusiform swelling and caseous material discharged out from small incision in nerve sheath. Leprotic neuropathy was suspected and confirmed by microbiology lab. Pure neurotic leprosy is extremely rare and nerve biopsy is the gold standard for diagnosis. There were 202,256 new leprosy cases registered globally in 2019 according to WHO (World Health Organization) figures, and disease can present decades after exposure. Leprotic neuropathy should be considered in the differential diagnosis of peripheral ulnar neuropathy even in temperate regions to avoid delay in diagnosis and undesirable sequalae.


Introduction
Ulnar neuropathy due to cubital tunnel syndrome is a common presentation in elective orthopaedic clinics with causes usually attributed to idiopathic chronic compression. However, rare diagnoses should be considered and the senior author has previously reported on unusual case of bilateral simultaneous ulnar nerve palsy [1]. We present a case of chronic insidious ulnar neuropathy with unusual intraoperative findings.

Case Presentation
A 52-year-old right hand dominant female presented to our upper limb clinic with a 2-year history of progressive left hand weakness and decreased sensation with difficulty with activities of daily living. She reported the beginning of her symptoms after incidental trauma to her left hand. Her hand was painful, swollen with limited movement especially of her ring finger. The x-ray done at this time showed an undisplaced fracture of 4th metacarpal. She was treated conservatively in Plaster of Paris (POP) cast for 4 weeks. A few days after removal of cast and starting her physio program, she complained of ongoing weakness with altered sensation in the little and ring fingers. She was noted to be generally fit and healthy without significant medical or family history. She was born in West Africa and had been living in Ireland for 20 years. She denied any history of recent travel outside the country. None of her close family members had any symptoms or signs suggestive of neurological disorders as per her knowledge.
Examination showed normal contour of the upper limbs without any apparent deformity. Mild generalized muscle wasting was noticed and attributed to previous time of immobilization in the POP cast. There were full painless movements of her cervical spine; skin looked healthy with normal temperature and circulation. Both ulnar and radial pulses were palpable. She maintained full function and power of her left shoulder and elbow; however, she was unable to make a full fist of her left hand. Grip  weakness of 2 kg was noticed using a Jamar dynamometer versus 30 kg on contralateral normal side. Light touch sensation was altered in the ulnar nerve distribution and inability to flex the PIPs and DIPs joints of the ring and little fingers against resistance. Froment's test was positive and there was a positive Tinel's sign at the cubital tunnel. On palpating the ulnar nerve with elbow flexion, there was mild tenderness but no thickening or instability noticed compared to the right side. Routine blood investigations including full blood count and inflammatory markers were normal. Nerve conduction studies confirmed the presence of significant ulnar neuropathy with axonal damage localized at the elbow (Tables 1  and 2). At this stage, severe ulnar nerve compression in the cubital tunnel was the most accepted diagnosis and no further investigations warranted.
She was scheduled for ulnar nerve release. At operation, the roof of the cubital tunnel was incised as routine. A fusiform swelling of the whole nerve was noted just proximal to medial epicondyle (Fig. 1a). A small longitudinal incision of the epineural sheath was made and caseous material discharged and swelling was considered a cold abscess (an abscess that lacks typical signs of inflammations like heat, fever, and pain) mostly due to mycobacterial infection (Fig. 1b).
Leprotic neuropathy was suspected and specimens were obtained for histology and microbiology including the caseous discharge and part of nerve sheath. Acid fast bacilli were not seen with direct microscopy but Mycobacterium leprae infection was identified in the regional lab using Sanger DNA sequencing. Culture for other mycobacteria was negative after 12 weeks. Our case was classified as paucibacillary (PB) and antimycobacterial combination therapy with Dapson and Rifampicin was commenced as per the World Health Organization (WHO) guidelines and classification on treatment of leprosy [2].
At her last clinic follow-up 4 months postoperative, patient has showed reasonable recovery of her symptoms specially her hand power with strength about 18 kg using the same dynamometer and no significant limitations in the activities of daily living.

Discussion and Conclusion
Leprosy is a chronic infectious disease caused by a slowly growing bacillus, Mycobacterium leprae, identified by G. H. A. Hansen in Norway in 1873 [3]. It was the first bacterium to be identified as causing disease in humans [4]. The natural immunity of the host determines the clinical and pathological manifestations of the disease which can take 20 years or more to appear [5]. Nerve infection in leprosy is due to persisting bacilli and their antigens in Schwann cells which can stimulate inflammatory episodes years after an initial infection. Untreated leprosy can cause damage to skin, nerves, limbs, and eyes. Ninety-five percent of people who contact Ulnar n Proximal Latera the organism do not develop clinical disease and extensive contact is necessary for disease spread [6]. Disease is common in India, Brazil and Indonesia but numbers of new cases have dropped dramatically in the last few decades [6]. Neuropathy with cutaneous lesions is a common presentation of leprosy and it is perhaps the best-known form of inflammatory neuropathy. The nerves in the upper limbs are more often affected than those of the lower. The most commonly involved nerves are the ulnar, median, posterior auricular, superficial radial, common fibular, superficial fibular and posterior tibia [7]. Isolated ulnar nerve disease represents 60% of mononeuritis cases. Pure neuritic leprosy (PNL) with mainly sensory symptoms is rare (4-8% of patient) [2] and nerve biopsy is the gold standard for diagnosis [6]. Nerve thickening and enlargement is usually found, although this was not clinically evident in our patient. The early recognition and prompt treatment of neural involvement is of paramount importance to avoid significant disability. However, delay in diagnosis (up to 82% of the cases) and misdiagnosis are common, as in other neurological conditions and 68% of patients had nerve damage resulting in disability [2]. Increasing migration from countries with high rates of leprosy to those with low rates will further compound the problem of unfamiliarity with the clinical picture of leprosy [2].
We report a rare presentation of leprosy in a patient without cutaneous or systemic manifestation (PNL). According to WHO guidelines on leprosy, any patient who has a thickened or enlarged peripheral nerve with loss of sensation must be considered to have leprosy [3]. There were 202,256 new leprosy cases registered globally in 2019 according to WHO figures, and disease can present decades after exposure [5]. In conclusion, leprotic neuropathy should be considered in the differential diagnosis of peripheral ulnar neuropathy even in temperate regions to avoid delay in diagnosis and undesirable sequalae.

Supplementary Information
The online version contains supplementary material available at https:// doi. org/ 10. 1007/ s42399-022-01254-6. Author Contribution P. H. made the diagnosis of ulnar nerve palsy and planned the surgery. M. A. suspected M. Leprae infection intraoperatively and sent specimens to microbiology laboratory to confirm the diagnosis. M. A. wrote the report after collecting the necessary information. P. H. supplied the clinical photos, did the English language corrections, and added some changes.

Declarations
Ethical Approval and Consent to participate No ethical committee approval is required for this case report.

Consent for Publication
Written informed consent was obtained from the patient.

Competing Interests
The authors declare no competing interests.