Ulnar Nerve Abscess – Leprosy

A 40 year known HIV positive female presented with diffuse swelling of left arm around elbow painful for last 15 days, it was initially pain less with an associated numbness of little finger since 6 months, numbness and swelling was increasing gradually. On examination a nodular swelling behind the elbow on the medial aspect with tenderness. Limited elbow extension. No any skin discoloration. 

MRI elbow joint advised with preference to ulnar nerve. 

MRI shows marked focal nodular enlargement of ulnar nerve at elbow joint, thickening of rest of the ulnar nerve with marked inflammation on STIR sequence in an adjacent muscle compartments and facial planes. 

Imaging wise possibility of Ulnar neuritis / Abscess was given and advised to rule out Leprosy clinically. 

Incision and drainage of the abscess done followed by culture and sensitivity test. Histopathology report mentions caseating epitheloid granuloma and giant cells. Disrupted native nerve fibers within and around the granuloma. Acid fast bacilli in singles and clusters consistent with tuberculoid Hansen’s disease.

Imaging and histopathological diagnosis : Ulnar nerve Abscess – Leprosy. 

Discussion: 

Leprosy is a chronic granulomatous infection, caused by mycobacterium leprae.

Primarily affecting the peripheral nerve trunks and cutaneous nerves.

Classically presents with neural or dermal signs and symptoms. 

Ulnar nerve is most commonly involved in fact Leprosy is the only disease in which abscess develop in nerve trunk. These abscesses are usually chronic cold abscess. 

Leprosy has a high prevalence in India of about 5 per 10000 populations with about 70% of globally recorded cases. The leprosy bacilli have a characteristic feature of nerve involvement, involvement of testis, lymph nodes, spleen, liver, larynx, bone marrow.

Contribution of imaging is limited in leprosy but reorganization of the condition is important by radiologist as management is different as clinically and imaging wise other dd often include nerve sheath tumor. 

Broadly there are three types of leprosy, the tuberculoid, lepromatous and borderline. The differentiation is based on symptoms, bacterial load and individual’s immune response.

In Tuberculoid leprosy the primarily affected nerves are pressure/trauma dependent  The most commonly involved nerve is ulnar nerve followed by median nerve, sural nerve, radial and branches of facial nerve.

In lepromatous leprosy the nerve damage is widespread and symmetrical with extensive intracutaneous nerve involvement and resembles symmetric polyneuropathy. Sensory loss occurs in the coolest areas of body like dorsum of hand and feet, ear, dorsum of fore arm and anterolateral parts of leg.

Borderline leprosy has characteristic of both tuberculoid and lepromatous.

Management is often surgical after failure of steroid treatment and that is Epineurotomy by multiple longitudinal incisions and external decompression to relive the internal pressure through out the involved segment.