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MI5.1-5 | Musculoskeletal, Skin & Soft-Tissue Infections — PBL Case

CLINICAL SETTING

Balu, a 42-year-old temple priest from a small village in Rajasthan, is brought to the district hospital by his family after 10 days of progressive illness. His family reports that during Diwali festivities 10 days ago, he sustained a small puncture wound on his right palm while hammering a nail for a deity's decoration. The wound was cleaned at home with turmeric paste and wrapped in cloth. Four days later he developed jaw stiffness and difficulty swallowing. Over the next 3 days he developed generalised stiffness of his entire body and painful muscle spasms triggered by any noise or touch. He has not been vaccinated — the family mentions he missed several childhood vaccination drives. On arrival to hospital, he is conscious but in severe distress, with trismus (jaw tightly locked), a board-like rigid abdomen, and periodic opisthotonus (arching of the back). Any sound or attempt to examine him triggers violent, painful generalised spasms. Temperature 38.2°C, HR 130/min, BP 160/90 mmHg. The wound on his palm shows a small, relatively benign-looking puncture with no surrounding cellulitis or discharge.

Trigger 1: The Locked Jaw and Rigid Body

On examination, the house officer notes: trismus so severe that a tongue depressor cannot be inserted, risus sardonicus (sardonic grin), rigid neck and abdomen, and intermittent, painful generalised spasms lasting 30–60 seconds each time the room door slams or a trolley passes by. The original wound on his palm is a 0.5 cm deep puncture wound with no visible pus and no surrounding erythema. Gram stain of wound swab: Gram-positive rods, slender, with a terminal spore giving a 'drumstick' appearance. The spore is round and bulges the rod at one end. Culture is set up anaerobically.

DISCUSSION POINTS

  • Based on the clinical features (trismus, risus sardonicus, opisthotonus, spasms triggered by stimuli) and the Gram stain finding of a drumstick-shaped rod, which organism is responsible? Describe its key morphological features and why its appearance on Gram stain is diagnostic.
  • The wound looks benign — no pus, no cellulitis. Yet this man is critically ill. Explain the concept of non-invasiveness in the context of this organism: why does a tiny puncture cause such systemic disease?
  • Trace the journey of the toxin from the wound to the spinal cord. Which specific synaptic protein does it cleave, and what is the consequence of this cleavage at the Renshaw cell? Why does this cause spastic paralysis rather than flaccid paralysis?
Click to reveal Trigger 2: Complications and Laboratory Investigations (discuss previous trigger first!)

Trigger 2: Complications and Laboratory Investigations

Balu is admitted to the ICU. Over the next 48 hours he develops: (a) episodes of autonomic instability — alternating hypertension/hypotension, profuse sweating, and tachycardia; (b) aspiration pneumonia; and (c) laryngospasm requiring emergency intubation. His family brings his 10-year-old son Kavi, who played with the same nail and has a similar but smaller puncture wound on his finger, now 6 days old. Kavi has no symptoms. Kavi's vaccination record shows 3 doses of DTP were received in infancy, with the last dose at 18 months. No booster since. Laboratory for Balu: WBC 18,000 (neutrophilia), CRP 140 mg/L, blood cultures — no growth. Anaerobic culture of the wound shows growth of an obligate anaerobe. ELISA for anti-tetanospasmin antibodies in Balu: not detectable.

DISCUSSION POINTS

  • Balu's blood cultures are negative and ELISA for anti-tetanospasmin is negative (despite severe disease). Explain why both findings are expected in tetanus — what does this tell us about the disease mechanism and how diagnosis is made?
  • Kavi (10 years old, 3 infant DTP doses, no booster since 18 months) has an identical wound but no symptoms. What determines whether a puncture wound leads to tetanus? Calculate his likely level of protection and decide whether he needs prophylaxis — and if so, which one?
  • Autonomic instability is a life-threatening complication of severe tetanus. Which part of the nervous system is affected and why? Name the neurotransmitters involved and one pharmacological agent used to manage autonomic storms in ICU.
Click to reveal Trigger 3: Diagnosis, Treatment, and Prevention (discuss previous trigger first!)

Trigger 3: Diagnosis, Treatment, and Prevention

Balu receives: IV metronidazole, human tetanus immunoglobulin (HTIG) 3,000 IU IM, ICU sedation with diazepam, wound debridement, and mechanical ventilation. After 3 weeks he is slowly weaned off the ventilator and discharged after 5 weeks. During Balu's ICU stay, a 65-year-old woman, Savitri, is admitted to the same district hospital from the same village with a 2-week history of a well-defined hypopigmented patch on her left cheek with total loss of sensation and dryness. She is a known leprosy patient who defaulted from treatment 5 years ago. She now has 2 new tender, erythematous nodules on her forearms and is febrile. The PHC Leprosy Officer visits and examines her.

DISCUSSION POINTS

  • For Balu — explain why HTIG was administered and why it must be given BEFORE wound debridement in this sequence. What does HTIG neutralise? Why can it not reverse his existing neurological deficits? When should tetanus toxoid also be given, and why is it not given simultaneously at the same site as HTIG?
  • For Savitri — she has a single anaesthetic patch (existing) + new tender nodules + fever after long default. The PHC officer identifies this as a lepra reaction. Classify the reaction type (Type 1 reversal reaction vs. Type 2 ENL) using the clinical features provided, and explain the immunological mechanism underlying each type.
  • Design a village-level prevention programme that would have prevented BOTH Balu's tetanus AND Savitri's leprosy relapse. Include: (a) specific vaccination strategy for tetanus, (b) leprosy contact tracing and chemoprophylaxis with a single-dose drug, and (c) one health behaviour message for each condition targeting rural communities.

Group Task Assignments

Group 1: Tetanus pathogenesis and toxin mechanism

  • Draw a labelled diagram tracing the path of tetanospasmin from wound to spinal cord, marking the retrograde axonal transport route, the inhibitory Renshaw interneuron, and the site of synaptobrevin cleavage.
  • Compare and contrast the mechanisms and clinical effects of tetanospasmin vs. botulinum toxin in a two-column table — include: site of action, protein cleaved, neurotransmitter blocked, clinical result (spastic vs. flaccid).

Competencies: MI5.1

Group 2: Leprosy immunology and reactions

  • Construct the Ridley-Jopling immunological spectrum of leprosy with all 5 poles/borderline types. For each, note: number of lesions, SSS result, lepromin test, histopathology (key feature), and nerve damage pattern.
  • Differentiate Type 1 (reversal) reaction from Type 2 (ENL) reaction in a structured table covering: immunological mechanism, clinical features, which leprosy type it occurs in, treatment, and whether MDT should be continued.

Competencies: MI5.5

Group 3: Prophylaxis and public health response

  • Draft a village-level outbreak response plan for a cluster of tetanus cases following a religious festival. Include: tetanus toxoid vaccination schedule for unvaccinated adults, HTIG indications, wound care advice, and a message in simple language for community health workers.
  • Prepare a leprosy contact management protocol for Savitri's household. Include: who gets screened, how (clinical + SSS), single-dose rifampicin chemoprophylaxis eligibility criteria, and follow-up schedule.

Competencies: MI5.1, MI5.5

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [MI5.1] What is the molecular mechanism by which tetanospasmin produces spastic paralysis, and why does botulinum toxin — acting on the same class of vesicle protein — cause the opposite clinical effect (flaccid paralysis)?
  2. [MI5.1] What is the biological rationale for the clinical rule: 'Human tetanus immunoglobulin must be administered BEFORE wound debridement'? What happens to free toxin after debridement if HTIG has not been given first?
  3. [MI5.5] What are the clinical, bacteriological, and immunological differences between Type 1 (reversal) and Type 2 (ENL) lepra reactions, and what are the implications for continuing or modifying MDT during each?
  4. [MI5.5] What is the WHO recommendation for single-dose rifampicin chemoprophylaxis for leprosy contacts, and what is the evidence base for its use in India?
  5. [MI5.2] Which organisms cause septic arthritis in a 10-year-old child vs. a 70-year-old with a prosthetic joint, and how does the route of infection (haematogenous vs. contiguous) differ between these two age groups?