A 58-year-old man from Delhi presents with a 3-month history of progressive proximal muscle weakness, myalgia, and difficulty climbing stairs. On examination, he has symmetric proximal muscle weakness (grade 3/5 in hip and shoulder girdles) and a violaceous rash over the knuckles and eyelids. Serum creatine kinase is elevated at 2800 IU/L. Chest X-ray reveals a 4 cm left hilar mass. Which paraneoplastic syndrome is most likely responsible for his clinical presentation?

Question

Accepted Answer

C. Dermatomyositis associated with lung cancer. ## Clinical Diagnosis: Paraneoplastic Dermatomyositis

### Key Clinical Features

**Key Point:** Dermatomyositis (DM) is a paraneoplastic syndrome characterized by the triad of proximal muscle weakness, elevated creatine kinase, and a pathognomonic violaceous (heliotrope) rash over the eyelids and Gottron's papules over the knuckles.

### Cancer Association

**High-Yield:** Lung cancer is the most common malignancy associated with paraneoplastic dermatomyositis in adults (especially in smokers from India). Other common associations include gastric, ovarian, and breast cancers.

### Pathophysiology

1. Autoimmune destruction of muscle fibers mediated by CD8+ T cells and antibodies against myositis-associated antigens (e.g., anti-Mi-2, anti-Jo-1)
2. Vasculitis of small blood vessels in muscle and skin
3. Perifascicular atrophy on muscle biopsy

### Diagnostic Criteria

| Feature | Dermatomyositis | LEMS | Osteoarthropathy |
|---------|-----------------|------|------------------|
| **Muscle weakness** | Proximal, symmetric | Proximal, with autonomic signs | None |
| **Rash** | Violaceous, pathognomonic | Absent | Absent |
| **CK elevation** | Marked (>1000 IU/L) | Normal or mild | Normal |
| **EMG findings** | Myopathic | Facilitation with high-frequency stimulation | N/A |
| **Associated cancer** | Lung, gastric, ovarian | Small cell lung cancer | Lung, gastric |

### Clinical Pearl

**Clinical Pearl:** Paraneoplastic DM in adults has a cancer association rate of 15–30%, making malignancy screening mandatory. The presence of anti-p155/140 antibodies (TIF1-γ) is highly specific for malignancy-associated DM.

### Management Approach

```mermaid
flowchart TD
  A[Suspected Paraneoplastic DM]:::outcome --> B{Confirm diagnosis}:::decision
  B -->|Elevated CK + EMG myopathy| C[Screen for malignancy]:::action
  C --> D[Chest CT, abdominal imaging]:::action
  D --> E{Cancer found?}:::decision
  E -->|Yes| F[Treat underlying cancer + immunosuppression]:::action
  E -->|No| G[Repeat imaging in 6 months]:::action
  F --> H[Corticosteroids + steroid-sparing agents]:::action
  H --> I[Clinical and biochemical improvement]:::outcome
```

### Mnemonic for Paraneoplastic Myositis

**Mnemonic:** **DM-LUNG** = Dermatomyositis–Lung cancer (most common), Gastric, Ovarian, Breast

[cite:Robbins 10e Ch 7]

Answer

A. Lambert-Eaton myasthenic syndrome

Answer

B. Hypertrophic osteoarthropathy

Answer

D. Paraneoplastic cerebellar degeneration

Explanation

Clinical Diagnosis: Paraneoplastic Dermatomyositis

Key Clinical Features

Cancer Association

Pathophysiology

Diagnostic Criteria

Clinical Pearl

Management Approach

Mnemonic for Paraneoplastic Myositis

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Feature	Dermatomyositis	LEMS	Osteoarthropathy
Muscle weakness	Proximal, symmetric	Proximal, with autonomic signs	None
Rash	Violaceous, pathognomonic	Absent	Absent
CK elevation	Marked (>1000 IU/L)	Normal or mild	Normal
EMG findings	Myopathic	Facilitation with high-frequency stimulation	N/A
Associated cancer	Lung, gastric, ovarian	Small cell lung cancer	Lung, gastric